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http://www.mdpi.com/2079-6412/5/3/465
Photocatalytic activity of Portland cement pastes blended with nanoparticles of titanium oxynitride (TiO2−xNy) was studied. Samples with different percentages of TiO2−xNy (0.0%, 0.5%, 1%, 3%) and TiO2 (1%, 3%) were evaluated in order to study their self-cleaning properties. The presence of nitrogen in the tetragonal structure of TiO2 was evidenced by X-ray diffraction (XRD) as a shift of the peaks in the 2θ axis. The samples were prepared with a water/cement ratio of 0.5 and a concentration of Rhodamine B of 0.5 g/L. After 65 h of curing time, the samples were irradiated with UV lamps to evaluate the reduction of the pigment. The color analysis was carried out using a Spectrometer UV/Vis measuring the coordinates CIE (Commission Internationale de l’Eclairage) L*, a*, b*, and with special attention to the reddish tones (Rhodamine B color) which correspond to a* values greater than zero. Additionally, samples with 0.5%, 1%, 3% of TiO2−xNy and 1%, 3% of TiO2 were evaluated under visible light with the purpose of determining the Rhodamine B abatement to wavelengths greater than 400 nm. The results have shown a similar behavior for both additions under UV light irradiation, with 3% being the addition with the highest photocatalytic efficiency obtained. However, TiO2−xNy showed activity under irradiation with visible light, unlike TiO2, which can only be activated under UV light.Coatings2015-07-3153Article10.3390/coatings50304654654762079-64122015-07-31doi: 10.3390/coatings5030465Juan CohenGermán GallegoJorge Tobónhttp://www.mdpi.com/2079-6412/5/3/425
This review presents the latest results of studies directed at photocatalyst coatings of titanium dioxide (TiO2) prepared by mechanical coating technique (MCT) and its application. Compared with traditional coating techniques, MCT is a simple, low cost and useful coating formation process, which is proposed and developed based on mechanical frictional wear and impacts between substrate materials and metal powder particles in the bowl of planetary ball mill. The formation process of the metal coatings in MCT includes four stages: The nucleation by adhesion, the formation and coalescence of discrete islands, formation and thickening of continuous coatings, exfoliation of continuous coatings. Further, two-step MCT was developed based on the MCT concept for preparing composite coatings on alumina (Al2O3) balls. This review also discusses the influence on the fabrication of photocatalyst coatings after MCT and improvement of its photocatalytic activity: oxidation conditions, coating materials, melt salt treatment. In this review, the oxidation conditions had been studied on the oxidation temperature of 573 K, 673 K, 773 K, 873 K, 973 K, 1173 K and 1273 K, the oxidation time of 0.5 h, 1 h, 3 h, 10 h, 15 h, 20 h, 30 h, 40 h, and 50 h. The photocatalyst coatings showed the highest photocatalytic activity with the oxidation condition of 1073 K for 15 h. The metal powder of Ti, Ni and Cr had been used as the coating materials. The composite metal powder could affect the surface structure and photocatalytic activity. On the other hand, the melt salt treatment with KNO3 is an effective method to form the nano-size structure and enhance photocatalytic activity, especially under visible light.Coatings2015-07-3053Review10.3390/coatings50304254254642079-64122015-07-30doi: 10.3390/coatings5030425Yun LuSujun GuanLiang HaoHiroyuki Yoshidahttp://www.mdpi.com/2079-6412/5/3/378
In this review, we discuss the basic concepts related to (co-)evaporation and (co)sputtering based fabrication methods and the electrical properties of polymer-metal nanocomposite films. Within the organic-inorganic hybrid nanocomposites research framework, the field related to metal-polymer nanocomposites is attracting much interest. In fact, it is opening pathways for engineering flexible composites that exhibit advantageous electrical, optical, or mechanical properties. The metal-polymer nanocomposites research field is, now, a wide, complex, and important part of the nanotechnology revolution. So, with this review we aim, starting from the discussion of specific cases, to focus our attention on the basic microscopic mechanisms and processes and the general concepts suitable for the interpretation of material properties and structure–property correlations. The review aims, in addition, to provide a comprehensive schematization of the main technological applications currently in development worldwide.Coatings2015-07-2953Review10.3390/coatings50303783784242079-64122015-07-29doi: 10.3390/coatings5030378Vanna TorrisiFrancesco Ruffinohttp://www.mdpi.com/2079-6412/5/3/366
Using ab initio alloy theory, we investigate the equilibrium bulk properties and elastic mechanics of the single bcc solid-solution AlxHf1−xNbTaTiZr (x = 0–0.7, 1.0) high entropy alloys. Ab initio predicted equilibrium volume is consistent with the available experiment. We make a detailed investigation of the alloying effect of Al and Hf on the equilibrium volume, elastic constants and polycrystalline elastic moduli. Results imply that the partial replacement Hf with Al increases the stability of the bcc phase and decreases the ductility of the AlxHf1−xNbTaTiZr HEAs. The inner ductility of Al0.4Hf0.6NbTaTiZr is predicted by the calculations of ideal tensile strength.Coatings2015-07-2953Article10.3390/coatings50303663663772079-64122015-07-29doi: 10.3390/coatings5030366Shaohui LiXiaodong NiFuyang Tianhttp://www.mdpi.com/2079-6412/5/3/357
Brick constitutes a significant part of the construction materials used in historic buildings around the world. This material was used in Architectural Heritage for structural scope, and even for building envelopes. Thus, components made of clay brick were subjected to weathering for a long time, and this causes their deterioration. One of the most important causes for deterioration is biodeterioration caused by algae and cyanobacteria. It compromises the aesthetical properties, and, at a later stage, the integrity of the elements. In fact, traditional products used for the remediation/prevention of biofouling do not ensure long-term protection, and they need re-application over time. The use of nanotechnology, especially the use of photocatalytic products for the prevention of organic contamination of building façades is increasing. In this study, TiO2-based photocatalytic nano-coatings were applied to ancient brick, and its efficiency towards biofouling was studied. A composed suspension of algae and cyanobacteria was sprinkled on the bricks’ surface for a duration of twelve weeks. Digital Image Analysis and colorimetric measurements were carried out to evaluate algal growth on specimens’ surfaces. Results show that photocatalytic nano-coating was able to inhibit biofouling on bricks’ surfaces. In addition, substrata (their porosity and roughness) clearly influences the adhesion of algal cells.Coatings2015-07-2853Article10.3390/coatings50303573573652079-64122015-07-28doi: 10.3390/coatings5030357Lorenzo GrazianiMarco D'Oraziohttp://www.mdpi.com/2079-6412/5/3/338
Suspension plasma spraying has become an emerging technology for the production of thermal barrier coatings for the gas turbine industry. Presently, though commercial systems for coating production are available, coatings remain in the development stage. Suitable suspension parameters for coating production remain an outstanding question and the influence of suspension properties on the final coatings is not well known. For this study, a number of suspensions were produced with varied solid loadings, powder size distributions and solvents. Suspensions were sprayed onto superalloy substrates coated with high velocity air fuel (HVAF) -sprayed bond coats. Plasma spray parameters were selected to generate columnar structures based on previous experiments and were maintained at constant to discover the influence of the suspension behavior on coating microstructures. Testing of the produced thermal barrier coating (TBC) systems has included thermal cyclic fatigue testing and thermal conductivity analysis. Pore size distribution has been characterized by mercury infiltration porosimetry. Results show a strong influence of suspension viscosity and surface tension on the microstructure of the produced coatings.Coatings2015-07-2453Article10.3390/coatings50303383383562079-64122015-07-24doi: 10.3390/coatings5030338Nicholas CurryKent VanEveryTodd SnyderJohann SusnjarStefan Bjorklundhttp://www.mdpi.com/2079-6412/5/3/326
Diamond-like carbon (DLC) coatings were deposited with a new direct ion deposition system using a novel 360 degree ion source operating at acceleration voltage between 4 and 8 kV. Cross-sectional TEM images show that the coatings have a three layered structure which originates from changes in the deposition parameters taking into account ion source condition, ion current density, deposition angles, ion sputtering and ion source movement. Varying structural growth conditions can be achieved by tailoring the deposition parameters. The coatings show good promise for industrial use due to their high hardness, low friction and excellent adhesion to the surface of the samples.Coatings2015-07-2453Article10.3390/coatings50303263263372079-64122015-07-24doi: 10.3390/coatings5030326Konrad SuschkeRené HübnerPeter MurmuPrasanth GuptaJohn FutterAndreas Markwitzhttp://www.mdpi.com/2079-6412/5/3/312
(Al0.34Cr0.22Nb0.11Si0.11Ti0.22)50N50 high-entropy nitride coatings prepared by reactive magnetron sputtering have been proved to have high hardness and superior oxidation resistance. Their thermal stability, adhesion strength, and cutting performance were investigated in this study. Hardness of the coating is 36 GPa, which only decreases slightly to 33 GPa after 900 °C annealing either in air or in vacuum for 2 h. No significant change in phase and microstructure were detected after annealing at 1000 °C. Rockwell C indentation and scratch tests shows that Ti interlayer provides a good adhesion between the nitride film and WC/Co substrates. In various milling tests, inserts coated with (Al0.34Cr0.22Nb0.11Si0.11Ti0.22)50N50 have evidently smaller flank wear depth than commercial inserts coated with TiN and TiAlN, even with their smaller thickness. Therefore, the (Al0.34Cr0.22Nb0.11Si0.11Ti0.22)50N50 coating has great potential in hard coating applications.Coatings2015-07-2353Article10.3390/coatings50303123123252079-64122015-07-23doi: 10.3390/coatings5030312Wan-Jui ShenMing-Hung TsaiJien-Wei Yehhttp://www.mdpi.com/2079-6412/5/3/293
Copper chalcopyrite is a promising candidate for a photocathode material for photoelectrochemical (PEC) water splitting because of its high half-cell solar-to-hydrogen conversion efficiency (HC-STH), relatively simple and low-cost preparation process, and chemical stability. This paper reviews recent advances in copper chalcopyrite photocathodes. The PEC properties of copper chalcopyrite photocathodes have improved fairly rapidly: HC-STH values of 0.25% and 8.5% in 2012 and 2015, respectively. On the other hand, the onset potential remains insufficient, owing to the shallow valence band maximum mainly consisting of Cu 3d orbitals. In order to improve the onset potential, we explored substituting Cu for Ag and investigate the PEC properties of silver gallium selenide (AGSe) thin film photocathodes for varying compositions, film growth atmospheres, and surfaces. The modified AGSe photocathodes showed a higher onset potential than copper chalcopyrite photocathodes. It was demonstrated that element substitution of copper chalcopyrite can help to achieve more efficient PEC water splitting.Coatings2015-07-1753Review10.3390/coatings50302932933112079-64122015-07-17doi: 10.3390/coatings5030293Hiroyuki KanekoTsutomu MinegishiKazunari Domenhttp://www.mdpi.com/2079-6412/5/3/278
This paper reports on an experimental and analytical investigation conducted into efficacy of the scraping shear-test method in estimating the shearing adhesive strength of a thermally sprayed coating. It was found that the critical average shear stress, the apparent failure strength of WC-Co thermal spray coating, depends on both the dimensions of the test piece and the loading position around the interface between the coating and the substrate. More specifically, the apparent critical shear stress decreased as the height and width of the test piece increased. In addition, the apparent critical shear stress increased with increasing coating thickness and with decreasing loading point distance measured from the interface. Consequently, the real adhesive strength of thermally sprayed coating could not be ascertained from these experimental results. Furthermore, most of the failure initiation points were inside the coating, as opposed to at the interface. This fact means that the results of the tests do not indicate the interfacial adhesive strength, but rather the shear strength of the coating. Three-dimensional finite element method (FEM) analysis showed that the distributions of the shearing stress at the loading points were virtually the same at failure, regardless of the dimensions of the test piece. These results suggest that the scraping test method needs a corresponding numerical analysis of the failure mode in order to produce reliable results and is not necessarily able to estimate the interfacial adhesive strength of thermally sprayed coating.Coatings2015-07-1553Article10.3390/coatings50302782782922079-64122015-07-15doi: 10.3390/coatings5030278Kenji Kanekohttp://www.mdpi.com/2079-6412/5/3/263
A series of polyester films doped with a hole transport molecule, p-diethylaminobenzaldehyde-1,1'-diphenylhydrazone (DEH), have been systematically exposed to ultraviolet radiation with a peak wavelength of about 375 nm. The electronic performance of the films, evaluated using time-of-flight and space-charge current injection methods, is observed to continuously degrade with increasing ultraviolet exposure. The degradation is attributed to photo cyclic oxidation of DEH that results in the creation of indazole (IND) molecules which function as bulk hole traps. A proposed model for the generation dynamics of the IND traps is capable of describing both the reduction in current injection and the associated time-of-flight hole mobility provided around 1% of the DEH population produce highly reactive photo-excited states which are completely converted to indazole during the UV exposure period. The rapid reaction of these states is incompatible with bulk oxygen diffusion-reaction kinetics within the films and is attributed to the creation of excited states within the reaction radius of soluble oxygen. It is suggested that encapsulation strategies to preserve the electronic integrity of the films should accordingly focus upon limiting the critical supply of oxygen for photo cyclic reaction.Coatings2015-07-0353Article10.3390/coatings50302632632772079-64122015-07-03doi: 10.3390/coatings5030263David Goldiehttp://www.mdpi.com/2079-6412/5/3/246
A model for spinodal decomposition must account for interface effects that include gradient and strain energy terms. The measurement of diffusion in the Cu-Ni(Fe) alloy for the special case of nanolaminate structured coatings is considered wherein the composition fluctuation is one-dimensional along &amp;lt;111&amp;gt;. An analytic approach is taken to model the kinetics of the transformation process that provides quantification of the strain energy dependence on the composition wavelength, as well as the intrinsic diffusivities and higher-order gradient-energy coefficients. The variation of the wave amplification factor R with wavenumber is modeled first to incorporate the boundary condition for growth at infinite wavelength. These results are used next to determine the gradient energy coefficients Kμ by modeling the interdiffusion coefficient ĎB variation with wavenumber, where a unique determination of the diffusion coefficient Ď is made. The value of the strain energy component that originates from interface strains associated with the epitaxial growth between layers is then determined by assessing the variation of wavelength-dependent amplification factors. A peak value of 9.4 × 107 J·m−3 for the strain energy is computed for Cu-Ni(Fe) nanolaminate coatings with 2–4 nm composition wavelengths.Coatings2015-06-2653Article10.3390/coatings50302462462622079-64122015-06-26doi: 10.3390/coatings5030246Alan Jankowskihttp://www.mdpi.com/2079-6412/5/3/232
The present study concerns the ecodesign of the application of an aqueous nano-TiO2 suspension on a porous limestone used in historical monuments with a spraying system through the LCA methodology, in order to define the most critical aspects of the process and to try to minimize the environmental burden during the implementation of the application process. Because of the limited knowledge currently available regarding the effects that nano-TiO2 may have on the environment or human health, a precautionary approach has been adopted in all life cycle steps, to assess the risk of having nanoparticle emissions from a nanocoating surface and for workers, who can come into contact with or inhale the nanoparticles released. The energy-intensive operations in the application stage greatly contribute to the total environmental damage, while the impact generated by nanoparticle emissions during the use phase contributes 2.9%. In addition, the self-cleaning and de-polluting transparent titania coating produces a benefit of −0.13%.Coatings2015-06-2553Article10.3390/coatings50302322322452079-64122015-06-25doi: 10.3390/coatings5030232Anna FerrariMartina PiniPaolo NeriFederica Bondiolihttp://www.mdpi.com/2079-6412/5/2/222
We proposed the application of titanium dioxide (TiO2) for the preservation of historical (architectural, monumental, archaeological) stone surfaces. Solar light can activate the photocatalytic effect of TiO2 nanoparticles: heterogeneous photocatalysis is the key factor for the development of self-cleaning, depolluting and biocidal treatments able to photochemically degrade external damaging materials and prolong the durability of treated substrates, maintaining their original aspect and limiting ordinary cleaning activities. In this study, TiO2 nanoparticles dispersed in an aqueous colloidal suspension were applied directly on travertine, a light-colored limestone, by spray-coating in order to obtain a nanometric film on stone samples. To assess the feasibility of use of TiO2, we studied the characteristics of the nanocoating-stone system by monitoring the microscopic features of the coatings, the aesthetical changes induced to coated surfaces and the self-cleaning efficiency. We also monitored the self-cleaning ability over time during an accelerated ageing process to evaluate the durability of TiO2-based treatments. We confirmed both compatibility and effectiveness of TiO2 coating in the short term, anyway its efficiency decreased after artificial ageing. Further studies are necessary to better evaluate and eventually improve the stability of self-cleaning efficiency over prolonged time for outdoor stone surfaces.Coatings2015-06-1952Article10.3390/coatings50202222222312079-64122015-06-19doi: 10.3390/coatings5020222Giovanni GoffredoPlacido Munafòhttp://www.mdpi.com/2079-6412/5/2/219
With the start of 2015, Coatings is instituting an annual award to recognize outstanding papers related to coatings and surface engineering that meet the aims, scope and high standards of this journal. [...]Coatings2015-06-1952Editorial10.3390/coatings50202192192212079-64122015-06-19doi: 10.3390/coatings5020219Alessandro Lavacchihttp://www.mdpi.com/2079-6412/5/2/195
Electrochemical deposition methods are increasingly being applied to advanced technology applications, such as microelectronics and, most recently, to energy conversion. Due to the ever growing need for device miniaturization and enhanced performance, vastly improved control of the growth process is required, which in turn necessitates a better understanding of the fundamental phenomena involved. This overview describes the current status of and latest advances in electrodeposition science and technology. Electrochemical growth phenomena are discussed at the macroscopic and atomistic scale, while particular attention is devoted to alloy and compound formation, as well as surface-limited processes. Throughout, the contribution of Professor Foresti and her group to the understanding of electrochemical interfaces and electrodeposition, is highlighted.Coatings2015-06-1752Review10.3390/coatings50201951952182079-64122015-06-17doi: 10.3390/coatings5020195Giovanni Zangarihttp://www.mdpi.com/2079-6412/5/2/186
A phase doppler anemometer (PDA) was used to determine the effects of evaporation on water spray for three rotary bell atomizer operational variable parameters: shaping air, bell speed and liquid flow. Shaping air was set at either 200 standard liters per minute (L/min) or 300 L/min, bell speed was set to 30, 40 or 50 thousand rotations per minute (krpm) and water flow rate was varied between 100, 200 or 300 cubic centimeters per minute (cm3/min). The total evaporation between 22.5 and 37.5 cm from the atomizer (cm3/s) was calculated for all the combinations of those variables. Evaporation rate increased with higher flow rate and bell speed but no statistically significant effects were obtained for variable shaping air on interactions between parameters.Coatings2015-05-2952Article10.3390/coatings50201861861942079-64122015-05-29doi: 10.3390/coatings5020186Rajan RayPaul HenshawNihar BiswasChris Sakhttp://www.mdpi.com/2079-6412/5/2/172
A comprehensive experimental investigation has been carried out into the role of film thickness variation and silver material formulation on printing capability in the screen printing process. A full factorial experiment was carried out where two formulations of silver materials were printed through a range of screens to a polyester substrate under a set of standard conditions. The materials represented a novel low silver content (45%–49%) polymer material and traditional high silver content (65%–69%) paste. The resultant prints were characterised topologically and electrically. The study shows that more cost effective use of the silver in the ink was obtained with the low silver polymer materials, but that the electrical performance was more strongly affected by the mesh being used (and hence film thickness). Thus, while optimum silver use could be obtained using materials with a lower silver content, this came with the consequence of reduced process robustness.Coatings2015-05-1252Article10.3390/coatings50201721721852079-64122015-05-12doi: 10.3390/coatings5020172Eifion JewellSimon HamblynTim ClaypoleDavid Gethinhttp://www.mdpi.com/2079-6412/5/2/142
Parylene, a non-critical, non-toxic layer material, which is not only a candidate for low-\(K\) dielectrics, but also well suited for long-term applications in the human body, has been deposited by (plasma-enhanced) chemical vapor deposition of the monomeric species. To that end, a specially-designed reactor exhibiting a cracker tube at its entrance, which serves as the upstream control, and a cooling trap in front of the downstream control has been applied. The process of polymerization has been traced and is explained by evaporating the dimeric species followed by dissociation in the cracker at elevated temperatures and, eventually, to the coating of the polymeric film in terms of thermodynamics. Alternatively, the process of dissociation has been accomplished applying a microwave plasma. In both cases, the monomerization is controlled by mass spectrometry. The window for surface polymerization could be clearly defined in terms of a factor of dilution by an inert gas for the chemical vapor deposition (CVD) case and in the case of plasma-enhanced chemical vapor deposition (PECVD), additionally by the power density. The characterization of the layer parameters has been carried out by several analytical tools: scanning electron microscopy and atomic force microscopy to determine the surface roughness and density and depth of voids in the film, which influence the layer capacitance and deteriorate the breakdown voltage, a bulk property. The main issue is the conduct against liquids between the two borders' hydrophilic and hydrophobic conduct, but also the super-hydrophobic character, which is the condition for the Lotus effect. The surface tension has been evaluated by contact angle measurements. Fourier-transform infrared spectroscopy has proven the conservation of all of the functional groups during polymerization.Coatings2015-05-0852Article10.3390/coatings50201421421712079-64122015-05-08doi: 10.3390/coatings5020142Andreas ReichelGerhard FranzMarkus-Christian Amannhttp://www.mdpi.com/2079-6412/5/2/124
Previous studies have shown that the barrier effect and the performance of organic-inorganic hybrid (OIH) sol-gel coatings are highly dependent on the coating deposition method as well as on the processing conditions. However, studies on how the coating deposition method influences the barrier properties in alkaline environments are scarce. The aim of this experimental research was to study the influence of experimental parameters using the dip-coating method on the barrier performance of an OIH sol-gel coating in contact with simulated concrete pore solutions (SCPS). The influence of residence time (Rt), a curing step between each dip step and the number of layers of sol-gel OIH films deposited on hot-dip galvanized steel to prevent corrosion in highly alkaline environments was studied. The barrier performance of these OIH sol-gel coatings, named U(400), was assessed in the first instants of contact with SCPS, using electrochemical impedance spectroscopy and potentiodynamic methods. The durability and stability of the OIH coatings in SCPS was monitored during eight days by macrocell current density. The morphological characterization of the surface was performed by Scanning Electronic Microscopy before and after exposure to SCPS. Glow Discharge Optical Emission Spectroscopy was used to investigate the thickness of the U(400) sol-gel coatings as a function of the number of layers deposited with and without Rt in the coatings thickness.Coatings2015-04-3052Article10.3390/coatings50201241241412079-64122015-04-30doi: 10.3390/coatings5020124Rita FigueiraCarlos SilvaElsa Pereirahttp://www.mdpi.com/2079-6412/5/2/115
A design of experiments approach was used to describe process parameter—spray pattern relationships in the Twin Wire Arc process using zinc feed stock in a TAFA 8835 (Praxair, Concord, NH, USA) spray torch. Specifically, the effects of arc current, primary atomizing gas pressure, and secondary atomizing gas pressure on spray pattern size, spray pattern flatness, spray pattern eccentricity, and coating deposition rate were investigated. Process relationships were investigated with the intent of maximizing or minimizing each coating property. It was determined that spray pattern area was most affected by primary gas pressure and secondary gas pressure. Pattern eccentricity was most affected by secondary gas pressure. Pattern flatness was most affected by primary gas pressure. Coating deposition rate was most affected by arc current.Coatings2015-04-2052Article10.3390/coatings50201151151232079-64122015-04-20doi: 10.3390/coatings5020115Allison HornerAaron HallJames McCloskeyhttp://www.mdpi.com/2079-6412/5/2/95
Dispersion of functional inorganic nano-fillers like TiO2 within polymer matrix is known to impart excellent photobactericidal activity to the composite. Epoxy resin systems with Ag+ ion doped TiO2 can have combination of excellent biocidal characteristics of silver and the photocatalytic properties of TiO2. The inorganic antimicrobial incorporation into an epoxy polymeric matrix was achieved by sonicating laboratory-made nano-scale anatase TiO2 and Ag-TiO2 into the industrial grade epoxy resin. The resulting epoxy composite had ratios of 0.5–2.0 wt% of nano-filler content. The process of dispersion of Ag-TiO2 in the epoxy resin resulted in concomitant in situ synthesis of silver nanoparticles due to photoreduction of Ag+ ion. The composite materials were characterized by DSC and SEM. The glass transition temperature (Tg) increased with the incorporation of the nanofillers over the neat polymer. The materials synthesized were coated on glass petri dish. Anti-biofilm property of coated material due to combined release of biocide, and photocatalytic activity under static conditions in petri dish was evaluated against Staphylococcus aureus ATCC6538 and Escherichia coli K-12 under UV irradiation using a crystal violet binding assay. Prepared composite showed significant inhibition of biofilm development in both the organisms. Our studies indicate that the effective dispersion and optimal release of biocidal agents was responsible for anti-biofilm activity of the surface. The reported thermoset coating materials can be used as bactericidal surfaces either in industrial or healthcare settings to reduce the microbial loads.Coatings2015-04-1452Article10.3390/coatings5020095951142079-64122015-04-14doi: 10.3390/coatings5020095Santhosh M.Kandasamy Natarajanhttp://www.mdpi.com/2079-6412/5/1/78
In this work, a morphological and structural characterization of a ternary Ag-Cu-Ge alloy of known composition was performed with the aim of evaluating how the passivation parameters (time and temperature) influence the morphological features of the material surface. A nanomechanical characterization was performed in order to correlate the morphology and microstructure of the alloy with its tarnish, wear, and scratch resistance. It was found that the addition of germanium to the alloy not only provides the material with tarnish and fire-stain resistance, but it also improves the scratch and wear resistance owing to the formation of a dense and stable thin oxide layer.Coatings2015-03-1351Article10.3390/coatings501007878942079-64122015-03-13doi: 10.3390/coatings5010078Antonio CusmaMarco SebastianiDaniele De FelicisAndrea BassoEdoardo Bemporadhttp://www.mdpi.com/2079-6412/5/1/63
This study numerically investigates cyclic thermal shock behavior of ZrO2/Ti functionally graded thermal barrier coatings (FG TBCs) based on a nonlinear mean-field micromechanical approach, which takes into account the time-independent and dependent inelastic deformation, such as plasticity of metals, creep of metals and ceramics, and diffusional mass flow at the ceramic/metal interface. The fabrication processes for the FG TBCs have been also considered in the simulation. The effect of creep and compositional gradation patterns on micro-stress states in the FG TBCs during thermal cycling has been examined in terms of the amplitudes, ratios, maximum and mean values of thermal stresses. The compositional gradation patterns highly affect thermal stress states in case of high creep rates of ZrO2. In comparison with experimental data, maximum thermal stresses, amplitudes and ratios of thermal stresses can be effective parameters for design of such FG TBCs subject to cyclic thermal shock loadings.Coatings2015-03-0551Article10.3390/coatings501006363772079-64122015-03-05doi: 10.3390/coatings5010063Hideaki Tsukamotohttp://www.mdpi.com/2079-6412/5/1/54
Ion layer gas reaction (ILGAR) method allows for deposition of Cl-containing and Cl-free In2S3 layers from InCl3 and In(OCCH3CHOCCH3)3 precursor salts, respectively. A comparative study was performed to investigate the role of Cl on the diffusion of Cu from CuSCN source layer into ILGAR deposited In2S3 layers. The Cl concentration was varied between 7 and 14 at.% by varying deposition parameters. The activation energies and exponential pre-factors for Cu diffusion in Cl-containing samples were between 0.70 to 0.78 eV and between 6.0 × 10−6 and 3.2 × 10−5 cm2/s. The activation energy in Cl-free ILGAR In2S3 layers was about three times less compared to the Cl-containing In2S3, and the pre-exponential constant six orders of magnitude lower. These values were comparable to those obtained from thermally evaporated In2S3 layers. The residual Cl-occupies S sites in the In2S3 structure leading to non-stoichiometry and hence different diffusion mechanism for Cu compared to stoichiometric Cl-free layers.Coatings2015-02-1651Article10.3390/coatings501005454622079-64122015-02-16doi: 10.3390/coatings5010054Henry WafulaMusembi RobinsonAlbert JumaThomas SakwaManasse KituiRodrigo AraozChristian-H. Fischerhttp://www.mdpi.com/2079-6412/5/1/39
Surface coatings formed by immersion in the ionic liquids (ILs) 1,3-dimethylimidazolium methylphosphonate (LMP101), 1-ethyl-3-methylimidazolium methylphosphonate (LMP102) and 1-ethyl-3-methylimidazolium ethylphosphonate (LEP102) on magnesium alloy AZ31B at 50 °C have been studied. The purpose of increasing the temperature was to reduce the immersion time, from 14 days at room temperature, to 48 hours at 50 °C. The abrasion resistance of the coated alloy was studied by microscratching under progressively increasing load, and compared with that of the uncoated material. The order of abrasion resistance as a function of the IL is LEP102 &amp;gt; LMP101 &amp;gt; LMP102, which is in agreement with the order obtained for the coatings grown at room temperature. The maximum reduction in penetration depth with respect to the uncovered alloy, of a 44.5%, is obtained for the sample treated with the ethylphosphonate LEP102. However, this reduction is lower than that obtained when the coating is grown at room temperature. This is attributed to the increased thickness and lower adhesion of the coatings obtained at 50 °C, particularly those obtained from methylphosphonate ionic liquids. The results are discussed from SEM-EDX and profilometry.Coatings2015-01-2851Article10.3390/coatings501003939532079-64122015-01-28doi: 10.3390/coatings5010039Tulia EspinosaJosé SanesMaría-Dolores Bermúdezhttp://www.mdpi.com/2079-6412/5/1/26
Atmospheric pressure plasma jet (APPJ) technology is a versatile technology that has been applied in many energy harvesting and storage devices. This feature article provides an overview of the advances in APPJ technology and its application to solar cells and batteries. The ultrafast APPJ sintering of nanoporous oxides and 3D reduced graphene oxide nanosheets with accompanying optical emission spectroscopy analyses are described in detail. The applications of these nanoporous materials to photoanodes and counter electrodes of dye-sensitized solar cells are described. An ultrashort treatment (1 min) on graphite felt electrodes of flow batteries also significantly improves the energy efficiency.Coatings2015-01-2751Review10.3390/coatings501002626382079-64122015-01-27doi: 10.3390/coatings5010026Jian-Zhang ChenCheng-Che HsuChing WangWei-Yang LiaoChih-Hung WuTing-Jui WuHsiao-Wei LiuHaoming ChangShao-Tzu LienHsin-Chieh LiChun-Ming HsuPeng-Kai KaoYao-Jhen YangI-Chun Chenghttp://www.mdpi.com/2079-6412/5/1/3
In almost all urban contexts and in many extra-urban conurbations, where road traffic is the main noise pollution source, the use of barriers is not allowed. In these cases, low-noise road surfaces are the most used mitigation action together with traffic flow reduction. Selecting the optimal surface is only the first problem that the public administration has to face. In the second place, it has to consider the issue of assessing the efficacy of the mitigation action. The purpose of the LEOPOLDO project was to improve the knowledge in the design and the characterization of low-noise road surfaces, producing guidelines helpful to the public administrations. Several experimental road surfaces were tested. Moreover, several measurement methods were implemented aiming to select those that are suitable for a correct assessment of the pavement performances laid as mitigation planning. In this paper, the experience gained in the LEOPOLDO project will be described, focusing on both the measurement methods adopted to assess the performance of a low-noise road surface and the criteria by which the experimental results have to be evaluated, presenting a comparison of the obtained results and their monitoring along time.Coatings2015-01-1551Article10.3390/coatings50100033252079-64122015-01-15doi: 10.3390/coatings5010003Gaetano LicitraMauro CerchiaiLuca TetiElena AscariFrancesco BiancoMarco Chetonihttp://www.mdpi.com/2079-6412/5/1/1
The editors of Coatings would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2014:[...]Coatings2015-01-0851Editorial10.3390/coatings5010001122079-64122015-01-08doi: 10.3390/coatings5010001 Coatings Editorial Officehttp://www.mdpi.com/2079-6412/4/4/796
Titanium dioxide thin films were deposited using a Tween® surfactant modified non-aqueous sol-gel method onto fluorine doped tin oxide glass substrates. The surfactant concentration and type in the sols was varied as well as the number of deposited layers. The as deposited thin films were annealed at 500 °C for 15 min before characterisation and photocatalytic testing with resazurin intelligent ink. The films were characterised using scanning electron microscopy, atomic force microscopy, X-ray diffraction, Raman spectroscopy and UV-Vis spectroscopy. Photocatalytic activity of the films was evaluated using a resazurin dye-ink test and the hydrophilicity of the films was analysed by water-contact angles measurements. Characterisation and photocatalytic testing has shown that the addition of surfactant in varying types and concentrations had a significant effect on the resulting thin film microstructure, such as changing the average particle size from 130 to 25 nm, and increasing the average root mean square roughness from 11 to 350 nm. Such structural changes have resulted in an enhanced photocatalytic performance for the thin films, with an observed reduction in dye half-life from 16.5 to three minutes.Coatings2014-12-1944Article10.3390/coatings40407967968092079-64122014-12-19doi: 10.3390/coatings4040796Ann-Louise AndersonRussell Binionshttp://www.mdpi.com/2079-6412/4/4/772
Tungsten-modified hydrogenated amorphous carbon coatings (a-C:H:W) were deposited on high speed steel by reactive magnetron sputtering of a tungsten carbide target in an argon-ethine atmosphere. The deposition parameters, sputtering power, bias voltage, argon and ethine flow rate, were varied according to a central composite design comprising 25 different parameter combinations. For comparison, a tungsten carbide coating was deposited, as well. During coating deposition, the process variables, total pressure, sputtering voltage and bias current, were measured as process characteristics. The thickness of the deposited coatings was determined using the crater grinding method, and the deposition rate was calculated. Young’s modulus E and indentation hardness HIT were characterized by means of nanoindentation. With E = 80 Coatings2014-12-1544Article10.3390/coatings40407727727952079-64122014-12-15doi: 10.3390/coatings4040772Harald HetznerChristoph SchmidStephan TremmelKarsten DurstSandro Wartzackhttp://www.mdpi.com/2079-6412/4/4/756
pH sensors are widely used in chemical and biological applications. Metal oxides-based pH sensors have many attractive features including insolubility, stability, mechanical strength, electrocatalyst and manufacturing technology. Various metal oxide thin films prepared by radio frequency (R.F.) magnetron sputtering have attractive features, including high pH sensitivity, fast response, high resolution, good stability and reversibility as well as potential for measuring pH under conditions that are not favourable for the commonly used glass electrodes-based pH sensors. In addition, thin film pH sensors prepared by R.F. magnetron sputtering offer many advantages, such as ease of packaging, low cost through the use of standard microfabrication processes, miniaturisation, capability of measuring pH at high temperatures, ruggedness and disposability. In this paper, recent development of R.F. magnetron sputtered thin films for pH sensing applications are reviewed.Coatings2014-12-0144Review10.3390/coatings40407567567712079-64122014-12-01doi: 10.3390/coatings4040756D. MauryaA. SardarinejadK. Alamehhttp://www.mdpi.com/2079-6412/4/4/747
Pd-F:SnO2 thin films have been prepared by spray pyrolysis technique. Optimization has been done by doping SnO2 with palladium at varying levels of concentration and then recording sheet resistance. The sheet resistivity has been observed to decrease gradually as at% Pd concentration is increased; an optimum sheet resistivity value of 2.71 × 10−2 Ω cm has been recorded. The decrease in sheet resistivity has been attributed to presence of Pd ions which contribute in increment of charge carrier density. Using the optimum value of at% Pd doping, the same procedure has been repeated to study the effect of fluorine on Pd:SnO2; an optimum value of 1.64 × 10−4 Ω cm sheet resistivity has been recorded. This decrease has been attributed to substitution of O− with those of fluorine hence improving charge carrier density. The effect of passivation has been studied by comparing as prepared, annealed and passivated Pd-F:SnO2 thin films. Annealing has been observed to decrease the sheet resistivity to 1.21 × 10−4 Ω cm, while passivation has the effect of increasing the sheet resistivity to 1.53 × 10−4 Ω cm which is attributed to effects resulting from annealing the samples in nitrogen gas atmosphere.Coatings2014-11-1944Article10.3390/coatings40407477477552079-64122014-11-19doi: 10.3390/coatings4040747Patrick MwatheRobinson MusembiMathew MunjiVictor OdariLawrence MungutiAlex NtilakigwaJohn NguuBoniface Muthokahttp://www.mdpi.com/2079-6412/4/4/732
Fluorine doped tin oxide (FTO) coatings have been prepared using the mid-frequency pulsed DC closed field unbalanced magnetron sputtering technique in an Ar/O2 atmosphere using blends of tin oxide and tin fluoride powder formed into targets. FTO coatings were deposited with a thickness of 400 nm on glass substrates. No post-deposition annealing treatments were carried out. The effects of the chemical composition on the structural (phase, grain size), optical (transmission, optical band-gap) and electrical (resistivity, charge carrier, mobility) properties of the thin films were investigated. Depositing FTO by magnetron sputtering is an environmentally friendly technique and the use of loosely packed blended powder targets gives an efficient means of screening candidate compositions, which also provides a low cost operation. The best film characteristics were achieved using a mass ratio of 12% SnF2 to 88% SnO2 in the target. The thin film produced was polycrystalline with a tetragonal crystal structure. The optimized conditions resulted in a thin film with average visible transmittance of 83% and optical band-gap of 3.80 eV, resistivity of 6.71 × 10−3 Ω·cm, a carrier concentration (Nd) of 1.46 × 1020 cm−3 and a mobility of 15 cm2/Vs.Coatings2014-10-3044Article10.3390/coatings40407327327462079-64122014-10-30doi: 10.3390/coatings4040732Ziad BanyaminPeter KellyGlen WestJeffery Boardmanhttp://www.mdpi.com/2079-6412/4/4/715
External walls made with hollow clay brick or block are widely used for their thermal, acoustic and structural properties. However, the performance of the bricks frequently does not conform with the minimum legal requirements or the values required for high efficiency buildings, and for this reason, they need to be integrated with layers of thermal insulation. In this paper, the thermal behavior of hollow clay block with low emissivity treatment on the internal cavity surfaces has been investigated. The purpose of this application is to obtain a reduction in the thermal conductivity of the block by lowering the radiative heat exchange in the enclosures. The aims of this paper are to indicate a methodology for evaluating the thermal performance of the brick and to provide information about the benefits that should be obtained. Theoretical evaluations are carried out on several bricks (12 geometries simulated with two different thermal conductivities of the clay), using a finite elements model. The heat exchange procedure is implemented in accordance with the standard, so as to obtain standardized values of the thermal characteristics of the block. Several values of emissivity are hypothesized, related to different kinds of coating. Finally, the values of the thermal transmittance of walls built with the evaluated blocks have been calculated and compared. The results show how coating the internal surface of the cavity provides a reduction in the thermal conductivity of the block, of between 26% and 45%, for a surface emissivity of 0.1.Coatings2014-10-1744Article10.3390/coatings40407157157312079-64122014-10-17doi: 10.3390/coatings4040715Roberto FiorettiPaolo Principihttp://www.mdpi.com/2079-6412/4/4/701
The surface of metal parts operating at high temperature in energy production and aerospace industry is typically exposed to thermal stresses and oxidation phenomena. To this aim, plasma spraying was employed to deposit NiCoCrAlYRe coatings on metal substrates. The effects of early-stage oxidation, at ~1100 °C, on their microstructure were investigated. The partial infiltration of oxygen through some open pores and microcracks embedded in coating microstructure locally assisted the formation of a stable Al2O3 scale at the splat boundary, while the diffusion of Cr and Ni and the following growth of Cr2O3, Ni(Cr,Al)2O4 and NiO were restricted to Al depleted isolated areas. At the same time, a continuous, dense and well adherent Al2O3 layer grew on the top-surface, and was somewhere supported by a thin mixed oxide scale mainly composed of Cr2O3 and spinels. Based on these results, the addition of Re to the NiCoCrAlY alloy is able to enhance the oxidation resistance.Coatings2014-10-1044Article10.3390/coatings40407017017142079-64122014-10-10doi: 10.3390/coatings4040701Giovanni GirolamoAlida BrentariEmanuele Serrahttp://www.mdpi.com/2079-6412/4/3/687
In this study, an electroactive polymer (EAP), poly(2,5-bis(N-methyl-N- hexylamino)phenylene vinylene) (BAM-PPV), was tested as an alternative to current hexavalent chromium (Cr(VI))-based Army wash primers. BAM-PPV was tested in both laboratory and field studies to determine its adhesive and corrosion-inhibiting properties when applied to steel and aluminum alloys. The Army Research Laboratory (ARL) tests showed that BAM-PPV combined with an epoxy primer and the Army chemical agent-resistant coating (CARC) topcoat met Army performance requirements for military coatings. After successful laboratory testing, the BAM-PPV was then field tested for one year at the Aberdeen Test Center (ATC). This field testing showed that BAM-PPV incorporated into the Army military coating survived with no delamination of the coating and only minor corrosion on the chip sites.Coatings2014-09-1543Article10.3390/coatings40306876877002079-64122014-09-15doi: 10.3390/coatings4030687Peter ZarrasChristopher MillerCindy WebberNicole AndersonJohn Stenger-Smithhttp://www.mdpi.com/2079-6412/4/3/670
In damp environments, indoor building materials are among the main proliferation substrates for microorganisms. Photocatalytic coatings, including nanoparticles of TiO2, could be a way to prevent microbial proliferation or, at least, to significantly reduce the amount of microorganisms that grow on indoor building materials. Previous works involving TiO2 have already shown the inactivation of bacteria by the photocatalysis process. This paper studies the inactivation of Escherichia coli bacteria by photocatalysis involving TiO2 nanoparticles alone or in transparent coatings (varnishes) and investigates different parameters that significantly influence the antibacterial activity. The antibacterial activity of TiO2 was evaluated through two types of experiments under UV irradiation: (I) in slurry with physiological water (stirred suspension); and (II) in a drop deposited on a glass plate. The results confirmed the difference in antibacterial activity between simple drop-deposited inoculum and inoculum spread under a plastic film, which increased the probability of contact between TiO2 and bacteria (forced contact). In addition, the major effect of the nature of the suspension on the photocatalytic disinfection ability was highlighted. Experiments were also carried out at the surface of transparent coatings formulated using nanoparticles of TiO2. The results showed significant antibacterial activities after 2 h and 4 h and suggested that improving the formulation would increase efficiency.Coatings2014-08-2243Article10.3390/coatings40306706706862079-64122014-08-22doi: 10.3390/coatings4030670Thomas VerdierMarie CoutandAlexandra BertronChristine Roqueshttp://www.mdpi.com/2079-6412/4/3/651
The photocatalytic activity and stability of thin, polycrystalline ZnO films was studied. The oxidative degradation of organic compounds at the ZnO surface results from the ultraviolet (UV) photo-induced creation of highly oxidizing holes and reducing electrons, which combine with surface water to form hydroxyl radicals and reactive oxygen species. Therefore, the efficiency of the electron-hole pair formation is of critical importance for self-cleaning and antimicrobial applications with these metal-oxide catalyst systems. In this study, ZnO thin films were fabricated on sapphire substrates via direct current sputter deposition of Zn-metal films followed by thermal oxidation at several annealing temperatures (300–1200 °C). Due to the ease with which they can be recovered, stabilized films are preferable to nanoparticles or colloidal suspensions for some applications. Characterization of the resulting ZnO thin films through atomic force microscopy and photoluminescence indicated that decreasing annealing temperature leads to smaller crystal grain size and increased UV excitonic emission. The photocatalytic activities were characterized by UV-visible absorption measurements of Rhodamine B dye concentrations. The films oxidized at lower annealing temperatures exhibited higher photocatalytic activity, which is attributed to the increased optical quality. Photocatalytic activity was also found to depend on film thickness, with lower activity observed for thinner films. Decreasing activity with use was found to be the result of decreasing film thickness due to surface etching.Coatings2014-08-1543Article10.3390/coatings40306516516692079-64122014-08-15doi: 10.3390/coatings4030651James MooreRobert LouderCody Thompsonhttp://www.mdpi.com/2079-6412/4/3/630
Suspension plasma spraying (SPS) has become an interesting method for the production of thermal barrier coatings for gas turbine components. The development of the SPS process has led to structures with segmented vertical cracks or column-like structures that can imitate strain-tolerant air plasma spraying (APS) or electron beam physical vapor deposition (EB-PVD) coatings. Additionally, SPS coatings can have lower thermal conductivity than EB-PVD coatings, while also being easier to produce. The combination of similar or improved properties with a potential for lower production costs makes SPS of great interest to the gas turbine industry. This study compares a number of SPS thermal barrier coatings (TBCs) with vertical cracks or column-like structures with the reference of segmented APS coatings. The primary focus has been on lifetime testing of these new coating systems. Samples were tested in thermo-cyclic fatigue at temperatures of 1100 °C for 1 h cycles. Additional testing was performed to assess thermal shock performance and erosion resistance. Thermal conductivity was also assessed for samples in their as-sprayed state, and the microstructures were investigated using SEM.Coatings2014-08-1543Article10.3390/coatings40306306306502079-64122014-08-15doi: 10.3390/coatings4030630Nicholas CurryKent VanEveryTodd SnyderNicolaie Markocsanhttp://www.mdpi.com/2079-6412/4/3/614
Surfaces are often coated with paint for improved aesthetics and protection; however, additional functionalities that impart continuous self-decontaminating and self-cleaning properties would be extremely advantageous. In this report, photochemical additives based on C60 fullerene were incorporated into polyurethane coatings to investigate their coating compatibility and ability to impart chemical decontaminating capability to the coating surface. C60 exhibits unique photophysical properties, including the capability to generate singlet oxygen upon exposure to visible light; however, C60 fullerene exhibits poor solubility in solvents commonly employed in coating applications. A modified C60 containing a hydrophilic moiety was synthesized to improve polyurethane compatibility and facilitate segregation to the polymer–air interface. Bulk properties of the polyurethane films were analyzed to investigate additive–coating compatibility. Coatings containing photoactive additives were subjected to self-decontamination challenges against representative chemical contaminants and the effects of additive loading concentration, light exposure, and time on chemical decontamination are reported. Covalent attachment of an ethylene glycol tail to C60 improved its solubility and dispersion in a hydrophobic polyurethane matrix. Decomposition products resulting from oxidation were observed in addition to a direct correlation between additive loading concentration and decomposition of surface-residing contaminants. The degradation pathways deduced from contaminant challenge byproduct analyses are detailed.Coatings2014-08-1343Article10.3390/coatings40306146146292079-64122014-08-13doi: 10.3390/coatings4030614Jeffrey LundinSpencer GilesRobert CozzensJames Wynnehttp://www.mdpi.com/2079-6412/4/3/602
Nowadays, cold technology for asphalt pavement in the field of road construction is considered as an alternative solution to conventional procedures from both an economic and environmental point of view. Among these techniques, bituminous slurry surfacing is obtaining an important role due to the properties of the obtained wearing course. The functional performance of this type of surfaces is directly related to its rough texture. Nevertheless, this parameter has a significant influence on the tire/road noise generation. To reduce this undesirable effect on the sound performance, new designs of elastic bituminous slurries have been developed. Within the FENIX project, this work presents the acoustical characterization of an experimental bituminous slurry with crumb rubber from wasted automobile tires incorporated by the dry process. The obtained results show that, under controlled operational parameters, the close proximity sound levels associated to the experimental slurry are considerably lower than those emitted by a conventional slurry wearing course. However, after one year of supporting traffic loads and different weather conditions, the evaluated bituminous slurry, although it conserves the original noise reduction properties in relation to the conventional one, noticeably increases the generated sound emission. Therefore, it is required to continue improving the design of experimental surfaces in order to enhance its long-term performance.Coatings2014-08-1143Article10.3390/coatings40306026026132079-64122014-08-11doi: 10.3390/coatings4030602Moisés BuenoJeanne LuongFernando TeránUrbano ViñuelaVíctor VázquezSantiago Pajehttp://www.mdpi.com/2079-6412/4/3/587
Anatase TiO2 thin films were deposited by DC reactive magnetron sputtering on glass substrates at 20 mTorr pressure in a flow of an Ar and O2 gas mixture. The O2 partial pressure (PO2) was varied from 0.65 mTorr to 1.3 mTorr to obtain two sets of films with different stoichiometry. The structure and morphology of the films were characterized by secondary electron microscopy, atomic force microscopy, and grazing-angle X-ray diffraction complemented by Rietveld refinement. The as-deposited films were amorphous. Post-annealing in air for 1 h at 500 °C resulted in polycrystalline anatase film structures with mean grain size of 24.2 nm (PO2 = 0.65 mTorr) and 22.1 nm (PO2 = 1.3 mTorr), respectively. The films sputtered at higher O2 pressure showed a preferential orientation in the &amp;lt;001&amp;gt; direction, which was associated with particle surfaces exposing highly reactive {001} facets. Films sputtered at lower O2 pressure exhibited no, or very little, preferential grain orientation, and were associated with random distribution of particles exposing mainly the thermodynamically favorable {101} surfaces. Photocatalytic degradation measurements using methylene blue dye showed that &amp;lt;001&amp;gt; oriented films exhibited approximately 30% higher reactivity. The measured intensity dependence of the degradation rate revealed that the UV-independent rate constant was 64% higher for the &amp;lt;001&amp;gt; oriented film compared to randomly oriented films. The reaction order was also found to be higher for &amp;lt;001&amp;gt; films compared to randomly oriented films, suggesting that the &amp;lt;001&amp;gt; oriented film exposes more reactive surface sites.Coatings2014-08-0843Article10.3390/coatings40305875876012079-64122014-08-08doi: 10.3390/coatings4030587B. StefanovL. Österlundhttp://www.mdpi.com/2079-6412/4/3/574
Metallization of ABS (acrylonitrile-butadiene-styrene) parts has been studied on flat part surfaces. These parts are fabricated on an FDM (fused deposition modeling machine) using the layer-wise deposition principle using ABS as a part material. Electroless copper deposition on ABS parts was performed using two different surface preparation processes, namely ABS parts prepared using chromic acid for etching and ABS parts prepared using a solution mixture of sulphuric acid and hydrogen peroxide (H2SO4/H2O2) for etching. After surface preparations using these routes, copper (Cu) is deposited electrolessly using four different acidic baths. The acidic baths used are 5 wt% CuSO4 (copper sulfate) with 15 wt% of individual acids, namely HF (hydrofluoric acid), H2SO4 (sulphuric acid), H3PO4 (phosphoric acid) and CH3COOH (acetic acid). Cu deposition under different acidic baths used for both the routes is presented and compared based on their electrical performance, scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS). The result shows that chromic acid etched samples show better electrical performance and Cu deposition in comparison to samples etched via H2SO4/H2O2.Coatings2014-08-0543Concept Paper10.3390/coatings40305745745862079-64122014-08-05doi: 10.3390/coatings4030574Azhar EqubalAnoop Soodhttp://www.mdpi.com/2079-6412/4/3/553
Photocatalytic concrete constitutes a promising technique to reduce a number of air contaminants such as NOx and VOC’s, especially at sites with a high level of pollution: highly trafficked canyon streets, road tunnels, the urban environment, etc. Ideally, the photocatalyst, titanium dioxide, is introduced in the top layer of the concrete pavement for best results. In addition, the combination of TiO2 with cement-based products offers some synergistic advantages, as the reaction products can be adsorbed at the surface and subsequently be washed away by rain. A first application has been studied by the Belgian Road Research Center (BRRC) on the side roads of a main entrance axis in Antwerp with the installation of 10.000 m² of photocatalytic concrete paving blocks. For now however, the translation of laboratory testing towards results in situ remains critical of demonstrating the effectiveness in large scale applications. Moreover, the durability of the air cleaning characteristic with time remains challenging for application in concrete roads. From this perspective, several new trial applications have been initiated in Belgium in recent years to assess the “real life” behavior, including a field site set up in the Leopold II tunnel of Brussels and the construction of new photocatalytic pavements on industrial zones in the cities of Wijnegem and Lier (province of Antwerp). This paper first gives a short overview of the photocatalytic principle applied in concrete, to continue with some main results of the laboratory research recognizing the important parameters that come into play. In addition, some of the methods and results, obtained for the existing application in Antwerp (2005) and during the implementation of the new realizations in Wijnegem and Lier (2010–2012) and in Brussels (2011–2013), will be presented.Coatings2014-07-3143Review10.3390/coatings40305535535732079-64122014-07-31doi: 10.3390/coatings4030553Elia BoonenAnne Beeldenshttp://www.mdpi.com/2079-6412/4/3/527
Investigations on the wetting, solubility and chemical composition of plasma polymer thin films provide an insight into the feasibility of implementing these polymeric materials in organic electronics, particularly where wet solution processing is involved. In this study, thin films were prepared from 1-isopropyl-4-methyl-1,4-cyclohexadiene (γ-Terpinene) using radio frequency (RF) plasma polymerization. FTIR showed the polymers to be structurally dissimilar to the original monomer and highly cross-linked, where the loss of original functional groups and the degree of cross-linking increased with deposition power. The polymer surfaces were hydrocarbon-rich, with oxygen present in the form of O–H and C=O functional groups. The oxygen content decreased with deposition power, with films becoming more hydrophobic and, thus, less wettable. The advancing and receding contact angles were investigated, and the water advancing contact angle was found to increase from 63.14° to 73.53° for thin films prepared with an RF power of 10 W to 75 W. The wetting envelopes for the surfaces were constructed to enable the prediction of the surfaces’ wettability for other solvents. The effect of roughness on the wetting behaviour of the films was insignificant. The polymers were determined to resist solubilization in solvents commonly used in the deposition of organic semiconducting layers, including chloroform and chlorobenzene, with higher stability observed in films fabricated at higher RF power.Coatings2014-07-3143Article10.3390/coatings40305275275522079-64122014-07-31doi: 10.3390/coatings4030527Jakaria AhmadKateryna BazakaMichael OelgemöllerMohan Jacobhttp://www.mdpi.com/2079-6412/4/3/508
In this work, a series of mono-and multilayer coatings were considered. They consisted of CrN and Cr prepared by physical vapor deposition with a cathodic arc. The most common steels for molds of plastics were chosen as substrates: X37CrMoV5-1 (SMV3), X2NiCoMo18-8-5 (MARVAL M1), X105CrCoMo18-2 (N690) and X40CrMo15 (X13T6). The samples were made with surface state conditions reproducing the main finishes required for molding of plastics: mirror, electro-eroded, sandblasted and ground finish. The coatings were characterized morphologically and chemically. The corrosion behavior of bare and coated steels was evaluated by electrochemical methods.Coatings2014-07-3143Article10.3390/coatings40305085085262079-64122014-07-31doi: 10.3390/coatings4030508Fabio CaiazzoValentina SistiStefano TrasattiSergio Trasattihttp://www.mdpi.com/2079-6412/4/3/497
Photocatalytic TiO2 coatings are famously known for their excellent self-cleaning behavior, where very thin water layer formed on the superhydrophilic surface can easily wash-off the dirt particles while flowing. Here we report the preparation of the optically transparent, adherent, highly wettable towards water and photocatalytic SiO2-TiO2 coatings on polycarbonate (PC) substrate for self-cleaning applications. The silica barrier layer was applied on UV-treated PC substrate before spin coating the SiO2-TiO2 coatings. The effect of different vol% of SiO2 in TiO2 and its influence on the surface morphology, mechanical stability, wettability, and photocatalytic properties of the coatings were studied in detail. The coatings prepared from 7 vol% of SiO2 in TiO2 showed smooth, crack-free surface morphology and low surface roughness compared to the coatings prepared from the higher vol% of SiO2 in TiO2. The water drops on this coating acquires a contact angle less than 10° after UV irradiation for 30 min. All the coatings prepared from different vol% (7 to 20) of SiO2 in TiO2 showed high transparency in the visible range.Coatings2014-07-2943Article10.3390/coatings40304974975072079-64122014-07-29doi: 10.3390/coatings4030497Sanjay LattheShanhu LiuChiaki TerashimaKazuya NakataAkira Fujishimahttp://www.mdpi.com/2079-6412/4/3/465
An experimental study of inert particle dispersion in an isothermal concentric air jet near field was conducted for cases of standard non-staggered and alternative staggered jet nozzles, each taken from a polymer powder flame deposition gun. The experimental work consisted of analysis of high speed digital images of the inert two phase isothermal jet flow, illuminated by a laser light sheet along and across the jet axis. The analysis of particle spread in the jet, represented by families of particle density distributions, clearly showed that the staggered nozzles resulted in a better-focused flow, with narrower distributions in the near field, and in the elimination of the recirculation zone that disrupted the particle flow in a non-staggered nozzle arrangement. In all cases, histograms of the cross-sectional particle area density were found to be approximately Gaussian. It was also found that there was a wide variation in the size and shape of the ground polymer particles used and these two characteristics caused a wide variation in the radial and axial velocities of the particles. Despite the differences between single-phase numerical simulations and experimental results, reported in Payne et al. [1], the introduction of particles into a numerical model produced satisfactory agreement with the particle velocities found experimentally.Coatings2014-07-2943Article10.3390/coatings40304654654962079-64122014-07-29doi: 10.3390/coatings4030465Graham PayneDarko MatovicEdward Grandmaisonhttp://www.mdpi.com/2079-6412/4/3/450
Mercury-supported, self-assembled monolayers (SAMs) of the sole dioleoylphosphatidylcholine (DOPC) and of a raft-forming mixture of DOPC, cholesterol (Chol) and palmitoylsphingomyelin (PSM) of (59:26:15) mol% composition, were investigated by electrochemical impedance spectroscopy (EIS), both in the absence and in the presence of the monosialoganglioside GM1. The impedance spectra of these four SAMs were fitted by a series of parallel combinations of a resistance and a capacitance (RC meshes) and displayed on plots of ωZ′ against −ωZ″, where Z′ and Z″ are the in-phase and quadrature components of the impedance and ω is the angular frequency. A comparison among these different impedance spectra points to the formation of GM1-rich gel phase microdomains within the lipid rafts of the DOPC/Chol/PSM mixture, thanks to the unique molecular-level smooth support provided by mercury, which allows EIS to detect the protruding gel phase microdomains by averaging them over a macroscopically large area.Coatings2014-07-1643Article10.3390/coatings40304504504642079-64122014-07-16doi: 10.3390/coatings4030450Lucia BecucciFrancesco VizzaYolanda DuarteRolando Guidellihttp://www.mdpi.com/2079-6412/4/3/433
TiO2 coatings deposited using reactive magnetron sputtering and spray coating methods, as well as Ag- and Mo-doped TiO2 coatings were investigated as self-cleaning surfaces for beverage processing. The mechanical resistance and retention of the photocatalytic properties of the coatings were investigated over a three-month period in three separate breweries. TiO2 coatings deposited using reactive magnetron sputtering showed better mechanical durability than the spray coated surfaces, whilst the spray-deposited coating showed enhanced retention of photocatalytic properties. The presence of Ag and Mo dopants improved the photocatalytic properties of TiO2 as well as the retention of these properties. The spray-coated TiO2 was the only coating which showed light-induced hydrophilicity, which was retained in the coatings surviving the process conditions.Coatings2014-07-1543Article10.3390/coatings40304334334492079-64122014-07-15doi: 10.3390/coatings4030433Parnia NavabpourSoheyla OstovarpourCarin TattershallKevin CookePeter KellyJoanna VerranKathryn WhiteheadClaire HillMari RaulioOuti Prihahttp://www.mdpi.com/2079-6412/4/3/416
The fabrication of a nanoporous gold (NPG)-based catalyst on a glassy carbon (GC) support results normally in large isolated and poorly adhering clusters that suffer considerable material loss upon durability testing. This work exploits thermochemical oxidation of GC, which, coupled with the utilization of some recent progress in fabricating continuous NPG layers using a Pd seed layer, aims to enhance the adhesion to the GC surface. Thermochemical oxidation causes interconnected pores within the GC structure to open and substantially improves the wettability of the GC surface, which are both beneficial toward the improvement of the overall quality of the NPG deposit. It is demonstrated that thermochemical oxidation neither affects the efficiency of the Au0.3Ag0.7 alloy (NPG precursor) deposition nor hinders the achievement of continuity in the course of the NPG fabrication process. Furthermore, adhesion tests performed by a rotating disk electrode setup on deposits supported on thermochemically-oxidized and untreated GCs ascertain the enhanced adhesion on the thermochemically-oxidized samples. The best adhesion results are obtained on a continuous NPG layer fabricated on thermochemically-oxidized GC electrodes seeded with a dense network of Pd clusters.Coatings2014-07-0943Article10.3390/coatings40304164164322079-64122014-07-09doi: 10.3390/coatings4030416Lori BrombergJiaxin XiaRyan RooneyNikolay Dimitrovhttp://www.mdpi.com/2079-6412/4/3/380
Thin film solar cells based on cadmium telluride (CdTe) are complex devices which have great potential for achieving high conversion efficiencies. Lack of understanding in materials issues and device physics slows down the rapid progress of these devices. This paper combines relevant results from the literature with new results from a research programme based on electro-plated CdS and CdTe. A wide range of analytical techniques was used to investigate the materials and device structures. It has been experimentally found that n-, i- and p-type CdTe can be grown easily by electroplating. These material layers consist of nano- and micro-rod type or columnar type grains, growing normal to the substrate. Stoichiometric materials exhibit the highest crystallinity and resistivity, and layers grown closer to these conditions show n → p or p → n conversion upon heat treatment. The general trend of CdCl2 treatment is to gradually change the CdTe material’s n-type electrical property towards i-type or p-type conduction. This work also identifies a rapid structural transition of CdTe layer at 385 ± 5 °C and a slow structural transition at higher temperatures when annealed or grown at high temperature. The second transition occurs after 430 °C and requires more work to understand this gradual transition. This work also identifies the existence of two different solar cell configurations for CdS/CdTe which creates a complex situation. Finally, the paper presents the way forward with next generation CdTe-based solar cells utilising low-cost materials in their columnar nature in graded bandgap structures. These devices could absorb UV, visible and IR radiation from the solar spectrum and combine impact ionisation and impurity photovoltaic (PV) effect as well as making use of IR photons from the surroundings when fully optimised.Coatings2014-06-2743Article10.3390/coatings40303803804152079-64122014-06-27doi: 10.3390/coatings4030380I. DharmadasaP. BinghamO. EchenduH. SalimT. DruffelR. DharmadasaG. SumanasekeraR. DharmasenaM. DergachevaK. MitK. UrazovL. BowenM. WallsA. Abbashttp://www.mdpi.com/2079-6412/4/2/356
This article presents a novel method for accelerated wear of squeegees used in screen printing and describes the development of mechanical tests which allow more in-depth measurement of squeegee properties. In this study, squeegees were abraded on the screen press so that they could be used for subsequent print tests to evaluate the effect of wear on the printed product. Squeegee wear was found to vary between different squeegee types and caused increases in ink transfer and wider printed features. In production this will lead to greater ink consumption, cost per unit and a likelihood of product failure. This also has consequences for the production of functional layers, etc., used in the construction of printed electronics. While more wear generally gave greater increases in ink deposition, the effect of wear differed, depending on the squeegee. There was a correlation between the angle of the squeegee wear and ink film thickness from a worn squeegee. An ability to resist flexing gave a high wear angle and presented a sharper edge at the squeegee/screen interface thus mitigating the effect of wear. There was also a good correlation between resistance to flexing and ink film thickness for unworn squeegees, which was more effective than a comparison based on Shore A hardness. Squeegee indentation at different force levels gave more information than a standard Shore A hardness test and the apparatus used was able to reliably measure reductions in surface hardness due to solvent absorption. Increases in ink deposition gave lower resistance in printed silver lines; however, the correlation between the amount of ink deposited and the resistance, remained the same for all levels of wear, suggesting that the wear regime designed for this study did not induce detrimental print defects such as line breakages.Coatings2014-06-1242Article10.3390/coatings40203563563792079-64122014-06-12doi: 10.3390/coatings4020356Christopher PhillipsDavid BeynonSimon HamblynGlyn DaviesDavid GethinTimothy Claypolehttp://www.mdpi.com/2079-6412/4/2/340
Nanomaterials in water present an array of identifiable potential hazards to ecological and human health. There is no general consensus about the influence of anionic or cationic charge on the toxicity of nanomaterials on environmental ecology. One challenge is the limited number of scalable technologies available for the removal of charged nanomaterials from water. A new method based on polymer coating has been developed in our laboratory for rapid sedimentation of nanomaterials in aqueous suspension. Using colloidal silica as a model inorganic oxide, coating of polyvinylpyrrolidone (PVP) around the SiO2 nanoparticles produced SiO2@PVP particles, as indicated by a linear increase of nephelometric turbidity. Purification of the water sample was afforded by total sedimentation of SiO2@PVP particles when left for 24 h. Characterization by capillary electrophoresis (CE) revealed nearly zero ionic charge on the particles. Further coating of polydopamine (PDA) around those particles in aqueous suspension produced an intense dark color due to the formation of SiO2@PVP@PDA. The SiO2@PVP@PDA peak appeared at a characteristic migration time of 4.2 min that allowed for quantitative CE-UV analysis to determine the original SiO2 concentration with enhanced sensitivity and without any ambiguous identity.Coatings2014-05-2042Article10.3390/coatings40203403403552079-64122014-05-20doi: 10.3390/coatings4020340Edward LaiZafar IqbalSherif Nourhttp://www.mdpi.com/2079-6412/4/2/329
The topic of the present experiments are transition metal diboride coatings of composition (Ti0.49W0.51)B2 and (Ti0.44W0.30Cr0.26)B2. The coatings were deposited on steel substrates using dc magnetron sputtering. We investigated how annealing in argon at elevated temperatures modifies microstructure. The as-deposited films are amorphous. Annealing between 700 and 1100 °C results in the formation of nano-crystalline precipitates with average grain diameters of about 10–50 nm. A TiC phase (Fm-3m; a ≈ 4.3 Å) is observed as the dominating precipitate phase. In addition, small amounts (10%–20%) of a Cr23C6 phase (Fm-3m; a ≈ 10.6 Å) are observed. In contrast to literature data on the same coatings deposited on silicon substrates, the formation of boride precipitate phases is strongly suppressed here. From investigations with X-ray diffractometry, electron microscopy and secondary ion mass spectrometry we conclude that the nanostructure of the coatings is formed by reactive phase formation of the boride coating with the carbon containing steel substrate.Coatings2014-05-0742Article10.3390/coatings40203293293392079-64122014-05-07doi: 10.3390/coatings4020329Aleksandra NewirkowezBenjamin CappiRainer TelleHarald Schmidthttp://www.mdpi.com/2079-6412/4/2/320
SnO2-Ag composite nanomaterials of mass ratio 1:4, 2:3, 3:2 and 4:1 were fabricated and tested for toxicity to E. coli using the pour-plate technique. The said nanomaterials were mixed with laminating fluid and then coated on glass slides. The intensity of UVA transmitted through the coated glass slides was measured. Results revealed that the 1:4 ratios of SnO2-Ag composite nanomaterials have the optimum toxicity to E. coli. Furthermore, the glass slides coated with SnO2 nanomaterial showed the lowest intensity of transmitted UVA.Coatings2014-05-0642Article10.3390/coatings40203203203282079-64122014-05-06doi: 10.3390/coatings4020320Gil SantosEduardo TibayanGwen CastillonElmer EstacioTakashi FuruyaAtsushi IwamaeKohji YamamotoMasahiko Tanihttp://www.mdpi.com/2079-6412/4/2/308
Ti1−xCrxN thin-film samples were sputter-deposited with lateral composition gradients x = 0.1–0.9 across each sample. In order to determine the effect of Cr content on oxidation, samples were air-oxidized at temperatures ranging from 650 to 950 °C. The extent and type of oxide formed was characterized using X-ray diffraction. Only minor oxidation was observed for the 650–750 °C temperature range. At 850 °C, films below x = 0.7 showed poor oxidation resistance, with the formation of TiO2 and Cr2O3 oxides, but little oxidation occurred above x = 0.7. At 950 °C, films above x = 0.7 again exhibited the best oxidation resistance. Chromium nitride films, which deposited as Cr2N, were found to begin oxidizing at 750 °C, indicating that the increased oxidation resistance of the higher-Cr Ti-Cr-N films can be attributed to the Ti-induced stabilization of the B1-structured phase. A compositionally-uniform film (x = 0.79) was also deposited and analyzed by XPS before and after oxidation. Oxidation resulted in primarily Cr2O3 at the surface, with some TiO2 also present, with the oxide richer in Cr than the starting film composition. These results suggested that at higher Cr compositions in the film, the oxidation mechanism was controlled by Cr diffusion to the surface.Coatings2014-04-3042Communication10.3390/coatings40203083083192079-64122014-04-30doi: 10.3390/coatings4020308James KrzanowskiDaniel Foleyhttp://www.mdpi.com/2079-6412/4/2/282
Cadmium chloride treatment is a key processing step identified in the late 1970s to drastically improve the solar to electric conversion efficiency of CdS/CdTe thin film solar cells. Although a large body of experimental results are available to date, this process is yet to be understood even after three decades of research. This paper reviews the experimental results available, presents some new clues leading to improved understanding and suggests key research areas necessary to fully understand this crucial processing step. Improved understanding will lead to further increase in conversion efficiency of CdS/CdTe solar cells well beyond 20%.Coatings2014-04-3042Review10.3390/coatings40202822823072079-64122014-04-30doi: 10.3390/coatings4020282I. Dharmadasahttp://www.mdpi.com/2079-6412/4/2/253
Usually, some severe efforts are required to obtain tribological parameters like Archard’s wear depth parameter kd. Complex tribological experiments have to be performed and analyzed. The paper features an approach where such parameters are extracted from effective interaction potentials in combination with more physical-oriented measurements, such as Nanoindentation and physical scratch. Thereby, the effective potentials are built up and fed from such tests. By using effective material potentials one can derive critical loading situations leading to failure (decomposition strength) for any contact situation. A subsequent connection of these decomposition or failure states with the corresponding stress or strain distributions allows the development of rather comprehensive tribological parameter models, applicable in wear and fatigue simulations, as demonstrated in this work. From this, a new relatively general wear model has been developed on the basis of the effective indenter concept by using the extended Hertzian approach for a great variety of loading situations. The models do not only allow to analyze certain tribological experiments, such as the well known pin-on disk test or the more recently developed nano-fretting test, but also to forward simulate such tests and even give hints for structured optimization or result in better component life-time prediction. The work will show how the procedure has to be applied in general and a small selection of practical examples will be presented.Coatings2014-04-2342Article10.3390/coatings40202532532812079-64122014-04-23doi: 10.3390/coatings4020253Norbert Schwarzerhttp://www.mdpi.com/2079-6412/4/2/231
A new, cost-efficient and on-site-applicable thermal spraying process for depositing NiAl metallic overlay or bond-coat coatings for high temperature applications by synthesizing the desired intermetallic phases in-flight during oxy-acetylene flame spraying is presented. Base-metal powders were used for spraying and, by adjusting the spraying conditions, excellent NiAl-based coatings were achieved on various substrates, including mild steel, stainless steel and aluminium alloys. Expensive, pre-alloyed or agglomerated powders are avoided and the method is very promising for in-situ work and repairs. We call the new method “Combustion-Assisted Flame Spraying” (CAFSY) and its viability has been demonstrated at a pre-industrial level for coating metallic substrates. The NiAl-based coatings produced by CAFSY exhibit very high integrity with good adhesion, very low porosity, high surface hardness and high erosion resistance at a substantially lower cost than equivalent coatings using pre-prepared alloy powders.Coatings2014-04-1742Article10.3390/coatings40202312312522079-64122014-04-17doi: 10.3390/coatings4020231Galina XanthopoulouAmalia MarinouGeorge VekinisAggeliki LekatouMichalis Vardavouliashttp://www.mdpi.com/2079-6412/4/2/214
In this study diamond like carbon (DLC) coatings with Si interlayers were deposited on 316L stainless steel with varying gas pressure and substrate bias voltage using plasma enhanced chemical vapor deposition (PECVD) technology. Coating and interlayer thickness values were determined using X-ray photoelectron spectroscopy (XPS) which also revealed the presence of a gradient layer at the coating substrate interface. Coatings were evaluated in terms of the hardness, elastic modulus, wear behavior and adhesion. Deposition rate generally increased with increasing bias voltage and increasing gas pressure. At low working gas pressures, hardness and modulus of elasticity increased with increasing bias voltage. Reduced hardness and modulus of elasticity were observed at higher gas pressures. Increased adhesion was generally observed at lower bias voltages and higher gas pressures. All DLC coatings significantly improved the overall wear resistance of the base material. Lower wear rates were observed for coatings deposited with lower bias voltages. For coatings that showed wear tracks considerably deeper than the coating thickness but without spallation, the wear behavior was largely attributed to deformation of both the coating and substrate with some cracks at the wear track edges. This suggests that coatings deposited under certain conditions can exhibit ultra high flexible properties.Coatings2014-04-0142Article10.3390/coatings40202142142302079-64122014-04-01doi: 10.3390/coatings4020214Liam WardFabian JungeAndreas LampkaMark DobbertinChristoph MewesMarion Wieneckehttp://www.mdpi.com/2079-6412/4/2/203
Copper oxide (Cu2O)-based heterojunction solar cells were fabricated by spin-coating and electrodeposition methods, and photovoltaic properties and microstructures were investigated. Zinc oxide (ZnO) and Cu2O were used as n- and p-type semiconductors, respectively, to fabricate photovoltaic devices based on In-doped tin oxide/ZnO/Cu2O/Au heterojunction structures. Short-circuit current and fill factor increased by aluminum (Al) doping in the ZnO layer, which resulted in the increase of the conversion efficiency. The efficiency was improved further by growing ZnO and Cu2O layers with larger crystallite sizes, and by optimizing the Al-doping by spin coating.Coatings2014-03-3142Article10.3390/coatings40202032032132079-64122014-03-31doi: 10.3390/coatings4020203Takeo OkuTetsuya YamadaKazuya FujimotoTsuyoshi Akiyamahttp://www.mdpi.com/2079-6412/4/1/162
Metalloid and metal based oxides are an almost unavoidable component in the majority of solar cell technologies used at the time of writing this review. Numerous studies have shown increases of ≥1% absolute in solar cell efficiency by simply substituting a given layer in the material stack with an oxide. Depending on the stoichiometry and whether other elements are present, oxides can be used for the purpose of light management, passivation of electrical defects, photo-carrier generation, charge separation, and charge transport in a solar cell. In this review, the most commonly used oxides whose benefits for solar cells have been proven both in a laboratory and industrial environment are discussed. Additionally, developing trends in the use of oxides, as well as newer oxide materials, and deposition technologies for solar cells are reported.Coatings2014-03-2441Review10.3390/coatings40101621622022079-64122014-03-24doi: 10.3390/coatings4010162Sonya Calnanhttp://www.mdpi.com/2079-6412/4/1/160
The editors of Coatings would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2013. [...]Coatings2014-02-2441Editorial10.3390/coatings40101601601612079-64122014-02-24doi: 10.3390/coatings4010160 Coatings Editorial Officehttp://www.mdpi.com/2079-6412/4/1/139
Diagnostic- and therapeutic release-aimed nanoparticles require the highest degree of biocompatibility. Some physical and chemical characteristics of such nanomaterials are often at odds with this requirement. For instance, metals with specific features used as contrast agents in magnetic resonance imaging need particular coatings to improve their blood solubility and increase their biocompatibility. Other examples come from the development of nanocarriers exploiting the different characteristics of two or more materials, i.e., the ability to encapsulate a certain drug by one core-material and the targeting capability of a different coating surface. Furthermore, all these “human-non-self” modifications necessitate proofs of compatibility with the immune system to avoid inflammatory reactions and resultant adverse effects for the patient. In the present review we discuss the molecular interactions and responses of the immune system to the principal nanoparticle surface modifications used in nanomedicine.Coatings2014-02-1241Review10.3390/coatings40101391391592079-64122014-02-12doi: 10.3390/coatings4010139Olimpia GamucciAlice BerteroMariacristina GagliardiGiuseppe Bardihttp://www.mdpi.com/2079-6412/4/1/121
The tribological protection of carbon fiber reinforced epoxy composites (CFC) is essential for broadening their use from structural to functional applications, e.g., to linear bearings in mechanical engineering. However, their wear resistance in sliding and rolling contacts is low. This work focusses on the possibility of improving their tribological properties by the application of thin hard multi-layered coatings. Chromium nitride (CrN) single layer and chromium-CrN multilayer coatings of ~4 µm thickness, partly finished with a 1 µm diamond-like carbon (DLC) top layer, were deposited by magnetron sputtering at low temperatures on soft CFC and for comparison of the mechanical behavior on comparatively hard austenitic steel substrates. Structural investigations showed especially that the multilayer coatings possess a very fine grained, columnar microstructure and a very low density of intercolumnar micro-cracks, while the single layer coatings possess a coarse structure. The indentation testing and the analysis of the deformed and fractured cross-sections revealed a tougher behavior with improved plastic deformability of the multilayers in comparison to CrN single layers. However, in wear testing only coatings with DLC top layers significantly improved the tribological material properties of CFC. This is due to the reduced shear forces in sliding on low-friction DLC coatings on the soft epoxy-based CFC, decreasing the total dynamic stresses during sliding under high loads.Coatings2014-02-1241Article10.3390/coatings40101211211382079-64122014-02-12doi: 10.3390/coatings4010121Juergen LacknerWolfgang WaldhauserLukasz MajorMarcin Kothttp://www.mdpi.com/2079-6412/4/1/98
Thermally-sprayed Fe-based coatings have shown their potential for use in wear applications due to their good tribological properties. In addition, these kinds of coatings have other advantages, e.g., cost efficiency and positive environmental aspects. In this study, the microstructural details and tribological performances of Fe-based coatings (Fe-Cr-Ni-B-C and Fe-Cr-Ni-B-Mo-C) manufactured by High Velocity Oxygen Fuel (HVOF) thermal spray process are evaluated. Traditional Ni-based (Ni-Cr-Fe-Si-B-C) and hard-metal (WC-CoCr) coatings were chosen as references. Microstructural investigation (field-emission scanning electron microscope FESEM and X-Ray diffractometry XRD) reveals a high density and low oxide content for HVOF Fe-based coatings. Particle melting and rapid solidification resulted in a metastable austenitic phase with precipitates of mixed carbides and borides of chromium and iron which lead to remarkably high nanohardness. Tribological performances were evaluated by means of the ball on-disk dry sliding wear test, the rubber-wheel dry particle abrasion test, and the cavitation erosion wear test. A higher wear resistance validates Fe-based coatings as a future alternative to the more expensive and less environmentally friendly Ni-based alloys.Coatings2014-01-2941Article10.3390/coatings4010098981202079-64122014-01-29doi: 10.3390/coatings4010098Andrea MilantiHeli KoivuluotoPetri VuoristoGiovanni BolelliFrancesco BozzaLuca Lusvarghihttp://www.mdpi.com/2079-6412/4/1/85
PEDOT:PSS electron-blocking layer, and PEDOT:PSS + P3HT:PCBM stacked layers are fabricated by ultrasonic atomization and characterized by scanning electron microscopy (SEM) and optical profilometry. The measured thicknesses based on SEM and optical profilometry are quite different, indicating the incapability of measurement techniques for non-uniform thin films. The thickness measurements are compared against theoretical estimations and a qualitative agreement is observed. Results indicate that using a multiple pass fabrication strategy results in a more uniform thin film. It was also found that the film characteristics are a strong function of solution concentration and spraying passes, and a weak function of substrate speed. Film thickness increases with solution concentration but despite the prediction of theory, the increase is not linear, indicating a change in the film porosity and density, which can affect physical and opto-electrical properties. Overall, while spray coating is a viable fabrication process for a wide range of solar cells, film characteristics can be easily altered by a change in process parameters.Coatings2014-01-2141Article10.3390/coatings401008585972079-64122014-01-21doi: 10.3390/coatings4010085Morteza EslamianJoshua Newtonhttp://www.mdpi.com/2079-6412/4/1/60
The capability to fabricate photovoltaic (PV) solar cells on a large scale and at a competitive price is a milestone waiting to be achieved. Currently, such a fabrication method is lacking because the effective methods are either difficult to scale up or expensive due to the necessity for fabrication in a vacuum environment. Nevertheless, for a class of thin film solar cells, in which the solar cell materials can be processed in a solution, up scalable and vacuum-free fabrication techniques can be envisioned. In this context, all or some layers of polymer, dye-sensitized, quantum dot, and copper indium gallium selenide thin film solar cells illustrate some examples that may be processed in solution. The solution-processed materials may be transferred to the substrate by atomizing the solution and carrying the spray droplets to the substrate, a process that will form a thin film after evaporation of the solvent. Spray coating is performed at atmospheric pressure using low cost equipment with a roll-to-roll process capability, making it an attractive fabrication technique, provided that fairly uniform layers with high charge carrier separation and transport capability can be made. In this paper, the feasibility, the recent advances and challenges of fabricating spray-on thin film solar cells, the dynamics of spray and droplet impaction on the substrate, the photo-induced electron transfer in spray-on solar cells, the challenges on characterization and simulation, and the commercialization status of spray-on solar cells are discussed.Coatings2014-01-2141Review10.3390/coatings401006060842079-64122014-01-21doi: 10.3390/coatings4010060Morteza Eslamianhttp://www.mdpi.com/2079-6412/4/1/37
Bacterial surface fouling is problematic for a wide range of applications and industries, including, but not limited to medical devices (implants, replacement joints, stents, pacemakers), municipal infrastructure (pipes, wastewater treatment), food production (food processing surfaces, processing equipment), and transportation (ship hulls, aircraft fuel tanks). One method to combat bacterial biofouling is to modify the topographical structure of the surface in question, thereby limiting the ability of individual cells to attach to the surface, colonize, and form biofilms. Multiple research groups have demonstrated that micro and nanoscale topographies significantly reduce bacterial biofouling, for both individual cells and bacterial biofilms. Antifouling strategies that utilize engineered topographical surface features with well-defined dimensions and shapes have demonstrated a greater degree of controllable inhibition over initial cell attachment, in comparison to undefined, texturized, or porous surfaces. This review article will explore the various approaches and techniques used by researches, including work from our own group, and the underlying physical properties of these highly structured, engineered micro/nanoscale topographies that significantly impact bacterial surface attachment.Coatings2014-01-1741Review10.3390/coatings401003737592079-64122014-01-17doi: 10.3390/coatings4010037Mary GrahamNathaniel Cadyhttp://www.mdpi.com/2079-6412/4/1/18
Thermally-sprayed alumina based materials, e.g., alumina-titania (Al2O3-TiO2), are commonly applied as wear resistant coatings in industrial applications. Properties of the coatings depend on the spray process, powder morphology, and chemical composition of the powder. In this study, wear resistant coatings from Al2O3 and Al2O3-13TiO2 powders were sprayed with plasma and high-velocity oxygen-fuel (HVOF) spray processes. Both, fused and crushed, and agglomerated and sintered Al2O3-13TiO2 powders were studied and compared to pure Al2O3. The coatings were tested for abrasion, erosion, and cavitation resistances in order to study the effect of the coating structure on the wear behavior. Improved coating properties were achieved when agglomerated and sintered nanostructured Al2O3-13TiO2 powder was used in plasma spraying. Coatings with the highest wear resistance in all tests were produced by HVOF spraying from fused and crushed powders.Coatings2014-01-0241Article10.3390/coatings401001818362079-64122014-01-02doi: 10.3390/coatings4010018Ville MatikainenKari NiemiHeli KoivuluotoPetri Vuoristohttp://www.mdpi.com/2079-6412/4/1/1
We formulated a latex ink for ink-jet deposition of viable Gram-negative bacterium Gluconobacter oxydans as a model adhesive, thin, highly bio-reactive microstructured microbial coating. Control of G. oxydans latex-based ink viscosity by dilution with water allowed ink-jet piezoelectric droplet deposition of 30 × 30 arrays of two or three droplets/dot microstructures on a polyester substrate. Profilometry analysis was used to study the resulting dry microstructures. Arrays of individual dots with base diameters of ~233–241 µm were obtained. Ring-shaped dots with dot edges higher than the center, 2.2 and 0.9 µm respectively, were obtained when a one-to-four diluted ink was used. With a less diluted ink (one-to-two diluted), the microstructure became more uniform with an average height of 3.0 µm, but the ink-jet printability was more difficult. Reactivity of the ink-jet deposited microstructures following drying and rehydration was studied in a non-growth medium by oxidation of 50 g/L D-sorbitol to L-sorbose, and a high dot volumetric reaction rate was measured (~435 g·L−1·h−1). These results indicate that latex ink microstructures generated by ink-jet printing may hold considerable potential for 3D fabrication of high surface-to-volume ratio biocoatings for use as microbial biosensors with the aim of coating microbes as reactive biosensors on electronic devices and circuit chips.Coatings2013-12-1941Article10.3390/coatings40100011172079-64122013-12-19doi: 10.3390/coatings4010001Marcello FidaleoNadia BortoneMark SchulteMichael Flickingerhttp://www.mdpi.com/2079-6412/3/4/268
Protective ultra-thin barrier films gather increasing economic interest for controlling permeation and diffusion from the biological surrounding in implanted sensor and electronic devices in future medicine. Thus, the aim of this work was a benchmarking of the mechanical oxygen permeation barrier, cytocompatibility, and microbiological properties of inorganic ~25 nm thin films, deposited by vacuum deposition techniques on 50 µm thin polyetheretherketone (PEEK) foils. Plasma-activated chemical vapor deposition (direct deposition from an ion source) was applied to deposit pure and nitrogen doped diamond-like carbon films, while physical vapor deposition (magnetron sputtering in pulsed DC mode) was used for the formation of silicon as well as titanium doped diamond-like carbon films. Silicon oxide films were deposited by radio frequency magnetron sputtering. The results indicate a strong influence of nanoporosity on the oxygen transmission rate for all coating types, while the low content of microporosity (particulates, etc.) is shown to be of lesser importance. Due to the low thickness of the foil substrates, being easily bent, the toughness as a measure of tendency to film fracture together with the elasticity index of the thin films influence the oxygen barrier. All investigated coatings are non-pyrogenic, cause no cytotoxic effects and do not influence bacterial growth.Coatings2013-12-1634Article10.3390/coatings30402682683002079-64122013-12-16doi: 10.3390/coatings3040268Juergen LacknerClaudia MeindlChristian WolfAlexander FianClemens KittingerMarcin KotLukasz MajorCaterina CzibulaChristian TeichertWolfgang WaldhauserAnnelie-Martina WeinbergEleonore Fröhlichhttp://www.mdpi.com/2079-6412/3/4/253
Polyvinylpyrrolidone (PVP) is a conventionally applied hydrophilic lubricious coating on catheter-based cardiovascular devices, used in order to ease movement through the vasculature. Its use as drug reservoir and transfer agent on drug-coated balloons (DCB) is therefore extremely promising with regard to the simplification of its approval as a medical device. Here, we developed a PVP-based coating for DCB, containing paclitaxel (PTX) as a model drug, and studied the impact of crosslinking via UV radiation on drug stability, wash off, and transfer during simulated use in an in vitro vessel model. We showed that crosslinking was essential for coating stability and needed to be performed prior to PTX incorporation due to decreased drug bioavailability as a result of photodecomposition and/or involvement in vinylic polymerization with PVP under UV radiation. Moreover, the crosslinking time needed to be carefully controlled. While short radiation times did not provide enough coating stability, associated with high wash off rates during DCB insertion, long radiation times lowered drug transfer efficiency upon balloon expansion. A ten minutes radiation of PVP, however, combined a minimized drug wash off rate of 34% with an efficient drug transfer of 49%, underlining the high potential of photochemically crosslinked PVP as a coating matrix for DCB.Coatings2013-12-0534Article10.3390/coatings30402532532672079-64122013-12-05doi: 10.3390/coatings3040253Svea PetersenIngo MinrathSebastian KauleJürgen KöcherKlaus-Peter SchmitzKatrin Sternberghttp://www.mdpi.com/2079-6412/3/4/243
The hardness, heat conductivity and low friction coefficient of microcrystalline diamond make it a suitable candidate for tribological applications. However, its roughness and high deposition temperature pose significant obstacles to these applications. We have successfully grown nanocrystalline diamond on steel at 400 °C by hot-filament chemical vapor deposition by employing a CrN interfacial layer. Nanocrystalline diamond combines hardness and surface smoothness required in tribological applications. Microcrystalline diamond and carbon nanotubes can also be grown by controlling the deposition parameters. The fabricated films were characterized with Raman spectroscopy, X-ray diffraction (XRD), Transmission electron microscopy (TEM), and scanning electron microscopy (SEM).Coatings2013-12-0234Article10.3390/coatings30402432432522079-64122013-12-02doi: 10.3390/coatings3040243Rafael VelázquezVictor NetoKishore UppireddiBrad WeinerGerardo Morellhttp://www.mdpi.com/2079-6412/3/4/208
This paper examines, experimentally and numerically, an isothermal coaxial air jet, created by an innovative nozzle design for an air propane torch, used for the thermal deposition of polymers. This design includes staggering the origins of the central and annular jets and creating an annular air jet with an inward radial velocity component. The experimental work used a Pitot tube to measure axial velocity on the jet centerline and in the fully developed flow. The static gauge pressure in the near field was also measured and found to be positive, an unexpected result. The numerical work used Gambit and Fluent. An extensive grid sensitivity study was conducted and it was found that results from a relatively coarse mesh were substantially the same as results from a mesh with almost 11 times the number of control volumes. A thorough evaluation of all of the RANS models in Fluent 6.3.26 found that the flow fields they calculated showed at most partial agreement with the experimental results. The greatest difference between numerical and experimental results was the incorrect prediction by all RANS models of a recirculation zone in the near field on the jet axis. Experimental work showed it did not exist.Coatings2013-11-0134Article10.3390/coatings30402082082422079-64122013-11-01doi: 10.3390/coatings3040208Graham PayneDarko MatovicEdward Grandmaisonhttp://www.mdpi.com/2079-6412/3/4/194
In this article we investigate the structural and photocatalytic properties of W-doped titanium dioxide coatings. TiO2-W thin films were deposited onto glass slides by reactive magnetron co-sputtering. The properties of the films were analyzed using such techniques as XRD, Raman spectroscopy, EDX, TEM, and surface profilometry. The photocatalytic properties of the coatings were assessed using the methylene blue (MB) degradation test under UV and fluorescent light sources. The methylene blue decomposition experiments showed that, at the optimum dopant concentration of tungsten, the photocatalytic activity can be improved by a factor of 6, compared to undoped titania. For the coatings discussed within this work, the optimum dopant concentration was determined to be 5.89 at.% of W. The results indicated that tungsten doping at this level extends the lifetime of the photogenerated charge carriers and significantly increases the photocatalyst surface area.Coatings2013-10-2534Article10.3390/coatings30401941942072079-64122013-10-25doi: 10.3390/coatings3040194Marina RatovaGlen WestPeter Kellyhttp://www.mdpi.com/2079-6412/3/4/177
Titanium dioxide (titania) is widely used as a photocatalyst for its moderate band gap, high photoactivity, recyclability, nontoxicity, low cost and its significant chemical stability. The anatase phase of titania is known to show the highest photocatalytic activity, however, the presence of this phase alone is not sufficient for sustained activity. In this study TiO2 coatings were deposited onto glass substrates by mid-frequency pulsed magnetron sputtering from metallic targets in reactive mode using a Full Face Erosion (FFE) magnetron, which allows the magnetic field to be modulated during the deposition process. The as-deposited coatings were analysed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and micro-Raman spectroscopy. Selected coatings were then annealed at temperatures in the range of 400–700 °C and re-analysed. The photocatalytic activity of the coatings was investigated through measurements of the degradation of organic dyes, such as methyl orange, under the influence of UV and fluorescent light sources. It has been demonstrated that, after annealing, the pulsed magnetron sputtering process produced photo-active surfaces and that the activity of the coatings under exposure to fluorescent lamps was some 35%–45% of that observed under exposure to UV lamps.Coatings2013-10-2534Article10.3390/coatings30401771771932079-64122013-10-25doi: 10.3390/coatings3040177Nick FarahaniPeter KellyGlen WestClaire HillVladimir Vishnyakovhttp://www.mdpi.com/2079-6412/3/3/166
Titanium dioxide thin films are durable, chemically stable, have a high refractive index and good electro/photochemical proprieties. Consequently, they are widely used as anti-reflective layers in optical devices and large area glazing products, dielectric layers in microelectronic devices and photo catalytic layers in self-cleaning surfaces. Titania coatings may have amorphous or crystalline structures, where three crystalline phases of TiO2 can be obtained: anatase, rutile and brookite, although the latter is rarely found. It is known, however, that the structure of TiO2 coatings is sensitive to deposition conditions and can also be modified by post-deposition heat treatments. In this study, titania coatings have been deposited onto soda-lime glass substrates by reactive sputtering from a metallic target. The magnetron was driven in mid-frequency pulsed DC mode. The as-deposited coatings were analysed by micro Raman spectroscopy, X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM). Selected coatings were annealed at temperatures in the range 200–700 °C and re-analysed. Whilst there was weak evidence of a nanocrystallinity in the as-deposited films, it was observed that these largely amorphous low temperature structures converted into strongly crystalline structures at annealing temperatures above 400 °C.Coatings2013-09-1033Article10.3390/coatings30301661661762079-64122013-09-10doi: 10.3390/coatings3030166Justyna Kulczyk-MaleckaPeter KellyGlen WestGregory ClarkeJohn Ridealghhttp://www.mdpi.com/2079-6412/3/3/153
The photocatalytic behavior of titania coatings is largely determined by their crystalline structure. Depending on deposition conditions, though, titania may form amorphous, brookite, anatase or rutile structures, with anatase or anatase/rutile mixed phase structures showing the highest levels of activity. Anatase is activated by UV light and, consequently, there is a great deal of interest in doping titania films to both increase activity and extend it into the visible range. In this study, titania and doped titania coatings have been deposited from blended oxide powder targets. This highly versatile and economical technique allows dopant levels to be readily varied. Using this technique, titania coatings doped with W, Nb and ZnFe2O4 have been deposited onto glass substrates by pulsed magnetron sputtering. The as-deposited coatings were analyzed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and micro-Raman spectroscopy. Selected coatings were then annealed at temperatures in the range of 400–700 °C and re-analyzed. Structural transformation of the titania coatings was initiated in the 500–600 °C range, with the coatings annealed at 700 °C having predominantly anatase structures. The photocatalytic activity of the coatings was assessed through measurements of the degradation of organic dyes, such as methyl orange, under the influence of UV and fluorescent light sources. It was found that, after annealing, coatings with photo-active surfaces were produced and that activity varied with dopant content. Activity levels under fluorescent light irradiation were up to 60% of the activity measured under UV irradiation.Coatings2013-08-1433Article10.3390/coatings30301531531652079-64122013-08-14doi: 10.3390/coatings3030153Nick FarahaniPeter KellyGlen WestMarina RatovaClaire HillVladimir Vishnyakovhttp://www.mdpi.com/2079-6412/3/3/140
A synthesized polymeric form of chitosan, electrochemically precipitated and photochemically modified, has been found to have significant value in removal of toxic chromate oxyanions from solution. Fourier Transform Infra-Red (FTIR), Raman and X-ray photoelectron spectroscopy (XPS) indicated that a significant percentage of the amine functional groups were oxidized to nitro groups as a result of reactions with hydroxyl ions formed in the electrochemical process with additional oxidation occurring as a result of exposure to ultra-violet light. The adsorption capacity of the modified chitosan for chromate was investigated in a batch system by taking into account effects of initial concentration, pH of the solution and contact time. Nitro-chitosan showed greater adsorption capacity towards Cr (VI) than other forms of chitosan, with a maximum adsorption of 173 mg/g. It was found that pH 3 is the optimum for adsorption, a Langmuir model is the best fit for the adsorption isotherm, and the kinetics of reaction followed a pseudo second order function. Overall, our results indicate that electrochemical modification of chitosan is an effective method to enhance the reactivity of chitosan towards metals.Coatings2013-07-1933Article10.3390/coatings30301401401522079-64122013-07-19doi: 10.3390/coatings3030140Prashant JhaGary HaladaScott McLennanhttp://www.mdpi.com/2079-6412/3/3/126
Undoped and aluminum-doped zinc oxide (AZO) thin films are prepared by the sol-gel process. Zinc acetate dihydrate, ethanol, and monoethanolamine are used as precursor, solvent, and stabilizer, respectively. In the case of AZO, aluminum nitrate nonahydrate is added to the precursor solution with an atomic percentage equal to 1 and 2 at.% Al. The multi thin layers are deposited by spin-coating onto glass substrates, and are transformed into ZnO upon annealing at 550 °C. Films display a strong preferential orientation, with high values for the Texture Coefficients (TC) of the (002) direction (TC(002) ≈ 3). The structural, morphological, and optical properties of the thin films as a function of aluminum content have been investigated using X-Ray Diffraction (XRD), Atomic Force Microscopy (AFM), and Scanning Electronic Microscopy (SEM). Waveguiding properties of the thin films have been also studied using m-lines spectroscopy. The results indicate that the films are monomodes at 632.8 nm with optical propagation optical losses estimated around 1.6 decibel per cm (dB/cm).Coatings2013-07-0333Article10.3390/coatings30301261261392079-64122013-07-03doi: 10.3390/coatings3030126Lamia ZnaidiTahar TouamDominique VrelNacer SoudedSana YahiaOvidiu BrinzaAlexis FischerAzzedine Boudriouahttp://www.mdpi.com/2079-6412/3/2/108
Tungsten is the prime candidate material for plasma facing components of future fusion devices. Plasma spraying, with its ability to coat large areas, including non-planar surfaces, with a significant thickness, is a prospective fabrication technology for components subject to moderate heat loads, e.g., the first wall of the Demonstration Reactor (DEMO). The functionality of such coatings is critically dependent on their adhesion to the underlying material. This in turn, is influenced by a variety of processing-related factors, chief among them being the state of the interface. In this study, the effects of two factors—surface roughness and the presence of thin interlayers—were investigated. Two different levels of roughness of steel substrates were induced by grit blasting, and two thin interlayers—titanium (Ti) and tungsten (W)—were applied by physical vapor deposition prior to plasma spraying of W by a Water Stabilized Plasma (WSP) torch. Coating adhesion was determined by a shear adhesion test. The structures of the coatings and the interfaces, as well as the characteristics of the fractured surfaces, were observed by SEM.Coatings2013-06-2132Article10.3390/coatings30201081081252079-64122013-06-21doi: 10.3390/coatings3020108Jiří MatějíčekMonika VilémováRadek MušálekPavel SachrJakub Horníkhttp://www.mdpi.com/2079-6412/3/2/98
Peptoids that are helical and partially water soluble have been shown to self-assemble into microspheres when the peptoid solution is dried on a silicon substrate. Such microsphere coatings have great potential for use in biosensor technologies, specifically to increase the surface area for binding. However, in order to be useful, the peptoids must consistently form uniform coatings. In this study we investigated the effects of various coating protocol parameters on the uniformity of the resulting peptoid microsphere coatings, including (i) solvent, (ii) administration technique, and (iii) drying environment. In addition, we investigated the robustness of the coatings as well as the potential for using a glass substrate. These studies show that uniform, robust peptoid microsphere coatings can be formed using protic solvents, a full coverage administration technique, and drying in open air on silicon or glass substrates.Coatings2013-06-2132Article10.3390/coatings3020098981072079-64122013-06-21doi: 10.3390/coatings3020098Melissa HebertDhaval ShahPhillip BlakeShannon Servosshttp://www.mdpi.com/2079-6412/3/2/82
A single splat is the building block of a thermal spray coating; thus, investigating single splats is essential to understanding thermal spray coatings and their properties. In this study, the morphology of flame sprayed ethylene methacrylic acid (EMAA) splats, deposited at various stand-off distances (SODs) onto glass and mild steel substrates were investigated using a scanning electron microscope, Leica M Stereo-microscope, the WYKO surface profiler and the ContourGT surface profiler. This work analyzed the effect of the process variables on EMAA splat morphology. The modeling of the temperature versus velocity (TV) map, the temperature versus stand-off distance (TS) map and the velocity versus stand-off distance (VS) map of EMAA single splat were presented.Coatings2013-06-1432Article10.3390/coatings302008282972079-64122013-06-14doi: 10.3390/coatings3020082Wei XieJames WangChristopher Berndthttp://www.mdpi.com/2079-6412/3/2/59
The transport behavior of electromagnetic radiation through a polymeric coating or composite is the basis for the material color, appearance, and overall electromagnetic signature. As multifunctional materials become more advanced and next generation in-service applications become more demanding, a need for predictive design of electromagnetic signature is desired. This paper presents various components developed and used in a computational suite for the study and design of electromagnetic radiation transport properties in polymeric coatings and composites. Focus is given to the treatment of the forward or direct scattering problem on surfaces and in bulk matrices of polymeric materials. The suite consists of surface and bulk light scattering simulation modules that may be coupled together to produce a multiscale model for predicting the electromagnetic signature of various material systems. Geometric optics ray tracing is used to predict surface scattering behavior of realistically rough surfaces, while a coupled ray tracing-finite element approach is used to predict bulk scattering behavior of material matrices consisting of microscale and nanoscale fillers, pigments, fibers, air voids, and other inclusions. Extension of the suite to color change and appearance metamerism is addressed, as well as the differences between discrete versus statistical material modeling.Coatings2013-04-1132Article10.3390/coatings302005959812079-64122013-04-11doi: 10.3390/coatings3020059Erik SapperBrian Hinderliterhttp://www.mdpi.com/2079-6412/3/1/49
TiO2 thin films were synthesized by sol-gel process: titanium tetraisopropoxide (TTIP) was dissolved in isopropanol, and then hydrolyzed by adding a water/isopropanol mixture with a controlled hydrolysis ratio. The as prepared sol was deposited by “dip-coating” on a glass substrate with a controlled withdrawal speed. The obtained films were annealed at 350 and 500 °C (2 h). The morphological properties of the prepared films were analyzed by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The optical waveguiding properties of TiO2 films were investigated for both annealing temperature using m-lines spectroscopy. The refractive indices and the film thickness were determined from the measured effective indices. The results show that the synthesized planar waveguides are multimodes and demonstrate low propagation losses of 0.5 and 0.8 dB/cm for annealing temperature 350 and 500 °C, respectively.Coatings2013-03-1131Article10.3390/coatings301004949582079-64122013-03-11doi: 10.3390/coatings3010049Tahar TouamLamia ZnaidiDominique VrelIva Ninova-KuznetsovaOvidiu BrinzaAlexis FischerAzzedine Boudriouahttp://www.mdpi.com/2079-6412/3/1/26
Continuous convective-sedimentation assembly (CCSA) is a deposition method that constantly supplies the coating suspension to the meniscus behind the coating knife by inline injection, allowing for steady-state deposition of ordered colloids (which may include particles or cells or live cell-particle blends) by water evaporation. The constant inflow of suspended particles available for transport to the drying front yields colloidal arrays with significantly larger surface areas than previously described and thus expands the ability of convective assembly to deposit monolayers or very thin films of multiple sizes of particles on large surfaces. Using sulfated polystyrene microspheres as a model system, this study shows how tunable process parameters, namely particle concentration, fluid sonication, and fluid density, influence coating homogeneity when the meniscus is continuously supplied. Fluid density and fluid flow-path sonication affect particle sedimentation and distribution. Coating microstructure, analyzed in terms of void space, does not vary significantly with relative humidity or suspended particle concentration. This study evaluated two configurations of the continuous convective assembly method in terms of ability to control coating microstructure by varying the number of suspended polymer particles available for transport to the coating drying front through variations in the meniscus volume.Coatings2013-02-0631Article10.3390/coatings301002626482079-64122013-02-06doi: 10.3390/coatings3010026Jessica JenkinsMichael FlickingerOrlin Velevhttp://www.mdpi.com/2079-6412/3/1/16
The pencil hardness of a two-component polyurethane coating was improved by adding halloysite nanotubes to the recipe at a weight fraction of less than 10%. The pencil hardness was around F for the unfilled coating and increased to around 2H upon filling. It was important to silanize the surface of the filler in order to achieve good coupling to the matrix. Sonicating the sample during drying also improved the hardness. Scanning electron micrographs suggest that the nanotubes are always well immersed into the bulk of the film. With a thickness between 10 and 20 µm, the optical clarity was good enough to clearly read letters through the film. The films can be used in applications where transparency is required.Coatings2013-01-1831Article10.3390/coatings301001616252079-64122013-01-18doi: 10.3390/coatings3010016Xin LiIrina NikiforowKatja PohlJörg AdamsDiethelm Johannsmannhttp://www.mdpi.com/2079-6412/3/1/1
Metallic biomaterials have been extensively used in orthodontics throughout history. Gold, stainless steel, cobalt-chromium alloys, titanium and its alloys, among other metallic biomaterials, have been part of the orthodontic armamentarium since the twentieth century. Metals and alloys possess outstanding properties and offer numerous possibilities for the fabrication of orthodontic devices such as brackets, wires, bands, ligatures, among others. However, these materials have drawbacks that can present problems for the orthodontist. Poor friction control, allergic reactions, and metal ionic release are some of the most common disadvantages found when using metallic alloys for manufacturing orthodontic appliances. In order to overcome such weaknesses, research has been conducted aiming at different approaches, such as coatings and surface treatments, which have been developed to render these materials more suitable for orthodontic applications. The purpose of this paper is to provide an overview of the coating and surface treatment methods performed on metallic biomaterials used in orthodontics.Coatings2012-12-2731Review10.3390/coatings30100011152079-64122012-12-27doi: 10.3390/coatings3010001Santiago ArangoAlejandro Peláez-VargasClaudia Garcíahttp://www.mdpi.com/2079-6412/2/4/235
This work surveys the structure, substructure and submicroporosity of Cu metal coatings following condensation both under the conditions of space flight of orbital stations (OS) and under Earth-based conditions. Small-angle X-ray scattering (SAXS) and the method of Ar low-temperature desorption were used for investigation. It has been shown that the condensates deposited in space contain less and relatively equiaxial submicropores (SMPs) distributed more homogeneously than Earth-based disperse films.Coatings2012-11-2024Article10.3390/coatings20402352352412079-64122012-11-20doi: 10.3390/coatings2040235Leonid SkatkovPetr CheremskoyValeriy GomozovBoris BayrachnyGennadiy TulskiySvetlana Deribohttp://www.mdpi.com/2079-6412/2/4/221
The scratch resistance of coatings used on two highly visible automotive applications (automotive bodies and window glazings) were examined and reviewed. Types of damage (scratch vs. mar), the impact on customers, and the causes of scratch events were investigated. Different exterior clearcoat technologies, including UV curable and self-healing formulations were reviewed, including results from nano- and macro-scratch tests. Polycarbonate hardcoat glazings were tested vs. annealed glass samples using a Taber abraser, with the resulting damage analyzed using transmitted haze measurements and optical profilometry. A correlation between the damage seen in glass samples (many smooth, shallow mars) and the best hardcoat samples (fewer, deeper scratches) and the haze measurements was discussed. Nano-scratch results showed similar fracture forces, but measurably improved mar resistance for the hardcoats/glass system compared to exterior clearcoats.Coatings2012-11-1224Review10.3390/coatings20402212212342079-64122012-11-12doi: 10.3390/coatings2040221Christopher SeubertKenneth NieteringMark NicholsRick WykoffShannon Bollinhttp://www.mdpi.com/2079-6412/2/4/210
It has been proposed that a resin coating can serve as a means to protect dental structure after preparation of the tooth for indirect restorations, sealing the exposed dentin. The resin coating is applied on the cut surfaces immediately after tooth preparation and before making an impression by assembling a dentin bonding system and a flowable composite. Resin coatings minimize pulp irritation and improve the bond strength between a resin cement and tooth when bonding the restoration to tooth. Recently, thin-film coating dental materials based on all-in-one adhesive technology were introduced for resin coating of indirect restorations. The thin coating materials are applied in a single clinical step and create a barrier-like film layer on the prepared dentin. The thin coatings play an important role in protecting the dentin from physical, chemical, and biological irritation. In addition, these thin-film coating materials reportedly prevent marginal leakage beneath inlays or crown restorations. In light of the many benefits provided by such a protective layer, these all-in-one adhesive materials may therefore also have the potential to cover exposed root dentin surfaces and prevent caries formation. In this paper, recent progress of the dental coating materials and their clinical applications are reviewed.Coatings2012-10-0124Review10.3390/coatings20402102102202079-64122012-10-01doi: 10.3390/coatings2040210Toru NikaidoRena TakahashiMeu AriyoshiAlireza SadrJunji Tagamihttp://www.mdpi.com/2079-6412/2/3/195
This paper presents nano-impact (low cycle fatigue) behavior of as-deposited amorphous nitinol (TiNi) thin film deposited on Si wafer. The nitinol film was 3.5 µm thick and was deposited by the sputtering process. Nano-impact tests were conducted to comprehend the localized fatigue performance and failure modes of thin film using a calibrated nano-indenter NanoTest™, equipped with standard diamond Berkovich and conical indenter in the load range of 0.5 mN to 100 mN. Each nano-impact test was conducted for a total of 1000 fatigue cycles. Depth sensing approach was adapted to understand the mechanisms of film failure. Based on the depth-time data and surface observations of films using atomic force microscope, it is concluded that the shape of the indenter test probe is critical in inducing the localized indentation stress and film failure. The measurement technique proposed in this paper can be used to optimize the design of nitinol thin films.Coatings2012-08-3123Article10.3390/coatings20301951952092079-64122012-08-31doi: 10.3390/coatings2030195Nadimul H. FaisalRehan AhmedRichard Fuhttp://www.mdpi.com/2079-6412/2/3/179
Dental biomaterials and natural products represent two of the main growing research fields, revealing plant-derived compounds may play a role not only as nutraceuticals in affecting oral health, but also in improving physico-chemical properties of biomaterials used in dentistry. Therefore, our aim was to collect all available data concerning the utilization of plant polysaccharides, proteins and extracts rich in bioactive phytochemicals in enhancing performance of dental biomaterials. Although compelling evidences are suggestive of a great potential of plant products in promoting material-tissue/cell interface, to date, only few authors have investigated their use in development of innovative dental biomaterials. A small number of studies have reported plant extract-based titanium implant coatings and periodontal regenerative materials. To the best of our knowledge, this review is the first to deal with this topic, highlighting a general lack of research findings in an interesting field which still needs to be investigated.Coatings2012-07-2623Review10.3390/coatings20301791791942079-64122012-07-26doi: 10.3390/coatings2030179Elena M. VaroniMarcello IritiLia Rimondinihttp://www.mdpi.com/2079-6412/2/3/160
Titanium nitride and/or nitrogen ion implanted coated dental materials have been investigated since the mid-1980s and considered in various applications in dentistry such as implants, abutments, orthodontic wires, endodontic files, periodontal/oral hygiene instruments, and casting alloys for fixed restorations. Multiple methodologies have been employed to create the coatings, but detailed structural analysis of the coatings is generally lacking in the dental literature. Depending on application, the purpose of the coating is to provide increased surface hardness, abrasion/wear resistance, esthetics, and corrosion resistance, lower friction, as well as greater beneficial interaction with adjacent biological and material substrates. While many studies have reported on the achievement of these properties, a consensus is not always clear. Additionally, few studies have been conducted to assess the efficacy of the coatings in a clinical setting. Overall, titanium nitride and/or nitrogen ion implanted coated dental materials potentially offer advantages over uncoated counterparts, but more investigation is needed to document the structure of the coatings and their clinical effectiveness.Coatings2012-07-2623Review10.3390/coatings20301601601782079-64122012-07-26doi: 10.3390/coatings2030160Youssef S. Al JabbariJennifer FehrmanAshley C. BarnesAngela M. ZapfSpiros ZinelisDavid W. Berzinshttp://www.mdpi.com/2079-6412/2/3/138
Different coatings are used in dentistry in an attempt to prevent caries, improve bonding of restorative materials to tooth tissues, and coat implant surfaces in efforts to speed up osseointegration. These are just a few of the many coating applications used in dentistry. The intention of this review is not to cover the entire field of different coatings used in dentistry, because that topic is just too big to be covered in one single paper. Therefore, this review aims to highlight some fundamental coating principles and present these principles to an audience consisting mainly of dentists. To do so, this review will focus on the fundamental principles of coatings, namely surface properties/adhesives in general, since these topics form the foundation for most coating procedures used in dentistry.Coatings2012-07-2623Review10.3390/coatings20301381381592079-64122012-07-26doi: 10.3390/coatings2030138Karl-Johan M. Söderholmhttp://www.mdpi.com/2079-6412/2/3/120
The aim of this study was to produce a 3D mesh of defect free electrospun cellulose acetate nanofibres and to use this to produce a prototype composite resin containing nanofibre fillers. This might find use as an aesthetic orthodontic bracket material or composite veneer for restorative dentistry. In this laboratory based study cellulose acetate was dissolved in an acetone and dimethylacetamide solvent solution and electrospun. The spinning parameters were optimised and lithium chloride added to the solution to produce a self supporting nanofibre mesh. This mesh was then silane coated and infiltrated with either epoxy resin or an unfilled Bis-GMA resin. The flexural strength of the produced samples was measured and compared to that of unfilled resin samples. Using this method cellulose acetate nanofibres were successfully electrospun in the 286 nm range. However, resin infiltration of this mesh resulted in samples with a flexural strength less than that of the unfilled control samples. Air inclusion during preparation and incomplete wetting of the nanofibre mesh was thought to cause this reduction in flexural strength. Further work is required to reduce the air inclusions before the true effect of resin reinforcement with a 3D mesh of cellulose acetate nanofibres can be determined.Coatings2012-07-1123Article10.3390/coatings20301201201372079-64122012-07-11doi: 10.3390/coatings2030120Stephen A. BoydBo SuJonathan R. SandyAnthony J. Irelandhttp://www.mdpi.com/2079-6412/2/3/95
The mechanical and biological properties of bone implants need to be optimal to form a quick and firm connection with the surrounding environment in load bearing applications. Bone is a connective tissue composed of an organic collagenous matrix, a fine dispersion of reinforcing inorganic (calcium phosphate) nanocrystals, and bone-forming and -degrading cells. These different components have a synergistic and hierarchical structure that renders bone tissue properties unique in terms of hardness, flexibility and regenerative capacity. Metallic and polymeric materials offer mechanical strength and/or resilience that are required to simulate bone tissue in load-bearing applications in terms of maximum load, bending and fatigue strength. Nevertheless, the interaction between devices and the surrounding tissue at the implant interface is essential for success or failure of implants. In that respect, coatings can be applied to facilitate the process of bone healing and obtain a continuous transition from living tissue to the synthetic implant. Compounds that are inspired by inorganic (e.g., hydroxyapatite crystals) or organic (e.g., collagen, extracellular matrix components, enzymes) components of bone tissue, are the most obvious candidates for application as implant coating to improve the performance of bone implants. This review provides an overview of recent trends and strategies in surface engineering that are currently investigated to improve the biological performance of bone implants in terms of functionality and biological efficacy.Coatings2012-07-0223Review10.3390/coatings2030095951192079-64122012-07-02doi: 10.3390/coatings2030095Ruggero BoscoJeroen Van Den BeuckenSander LeeuwenburghJohn Jansen